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Introduction

This is a description of how to decode AIVDM/AIVDO sentences. It collects and integrates information from publicly available sources and is intended to assist developers of open-source software for interpreting these messages.

AIVDM/AIVDO sentences are emitted by receivers for AIS, the marine Automatic Identification System. AIS transmitters are fitted to vessels, navigation markers, and certain types of shore station. They periodically squawk their position (and course, when applicable), using TDMA (Time Division Multiple Access) technology similar to the way cellphones do to avoid mutual interference. AIS receivers make this data available for navigation, anti-collision systems, and other uses.

The International Maritime Organization’s (IMO) International Convention for the Safety of Life at Sea (SOLAS) requires operating AIS transmitters on all international cargo vessels of more than 300 tons displacement, all cargo vessels of more than 500 tons displacement, and all passenger vessels; see [SOLAS] for details. Individual maritime nations may have stricter and more detailed rules: for those obtaining in U.S. waters, see [US-REQUIREMENTS].

AIS receivers report ASCII data packets as a byte stream over serial or USB lines, using the NMEA 0183 or NMEA 2000 data formats. The RS422 variant of serial specified as a physical layer by NMEA 0183 is common in marine navigation systems; there may be a "pilot plug" [PILOTPLUG] which converts to USB. Alternatively, newer AIS receivers may report directly over RS232 or USB.

AIS packets have the introducer "!AIVDM" or "!AIVDO"; AIVDM packets are reports from other ships and AIVDO packets are reports from your own ship.

A lengthy description of AIS, focusing on the goals and history of the system, but not describing the data protocols in any detail, can be found at [AIS].

Standards

Multiple standards bear on the AIVDM/AIVDO format. This document exists because assembling them into a complete picture is technically difficult and was long impeded by legal barriers as well.

ITU Recommendation M.1371, "Technical Characteristics for a Universal Shipborne Automatic Identification System Using Time Division Multiple Access" [ITU1371], issued in 2001, first described the bit-level format of AIS radio messages. This standard was proprietary and expensive when issued. I did not have access to it or any of its followup revisions while assembling versions of this document up to 1.29.

ITU-R M.1371 was expanded and clarified by "IALA Technical Clarifications on Recommendation ITU-R M.1371-1" [IALA], which is freely available.

There have been three minor revisions of ITU-R M.1371 since it was originally issued. These add interpretations to packet bit fields that were previously marked "spare" and "regional reserved". ITU-R M.1371 revision 4 became available for free download, apparently at some point in early 2011, well after most of this document was assembled.

The ASCII format for AIVDM/AIVDO representations of AIS radio messages seems to have been set by IEC-PAS 61162-100, "Maritime navigation and radiocommunication equipment and systems" [IEC-PAS]. It is proprietary and I have not looked at it. Various public sources indicate that it has been "harmonized" with some version of NMEA 0183, which I also have not looked at because it too is proprietary and expensive, and surrounded by rapacious attack lawyers.

Information Sources

Together, the IALA Technical Clarifications at [IALA] and the Coast Guard’s AIS pages at [NAVCEN] describe AIS message payloads type 1-24 almost completely. Certain specialized binary messages of types 6 and 8 defined by the International Maritime Organization are described in [IMO236] and [IMO289]. The detail information on payload formats in this document is mostly derived from these public sources.

Kurt Schwehr is a research scientist at the Center for Coastal and Ocean Mapping at the University of New Hampshire. Much of his research involves AIS. His work blog at [Schwehr] contains sample messages and descriptions of AIS operation in the wild that shed light on various obscure corners of the specification. He has explained the otherwise undocumented Repeat Indicator field and USCG extended AIVDM to me by email. He also communicated some critical information from [IEC-PAS], and supplied information about new messages and fields in ITU-1371-3.

Descriptions of messages 25 and 26 are based on AIS transceiver vendor documentation was originally forwarded to me by a source wishing to remain anonymous; I later checked them against ITU1371-4. Message type 27 was described in ITU1371-4 and added here after that became a freely available download.

Should you set out to write a decoder using this document, you are likely to find that one of your challenges is finding enough AIS packet data to make an effective regression test — especially if you live out of line of sight of any ship traffic and would get nothing from running an AIS receiver. Fortunately, various AIS sites offer live feeds over the Internet that aggregate AIS streams from all over the world. Some charge subscriptions; others offer time-delayed access for free and charge for a real-time feed. Still others are pool sites; you join by contributing your feed and receive all feeds.

AIS Hub ([AISHUB]) is a free, public AIS feed pool. It provides exchange of AIS data in raw NMEA format; all AISHub members share their own received AIS data and receive the merged feed from all other participating parties. It is open-source friendly, offering a Linux port in source of its software for collecting and forwarding AIS data. Peter Stoyanov and the other AIS Hub principals have generously donated a live feed to the GPSD project despite the fact that I live 60 miles inland and cannot send them anything interesting.

Some of what this document explains about the quirks of real-world encoders comes from examples provided by Kurt Schwehr. Other such information, especially for the less common sentences, comes from inspection of sentences forwarded to me from AIS Hub by various interested parties, and more recently from AIS Hub itself.

Improving This Document

To avoid copyright difficulties, I rely only on freely redistributable public documents and paraphrased reports from people who have seen the relevant proprietary standards. If you are such a person, please help by reporting the following to be included in future versions of this document:

  • Sample sentences of types 16-17, 22-23, and 25-27.

  • Sample sentences of type 6 and 8 conforming to [IMO236], [IMO289], and [INLAND].

For verification purposes, I need the raw sentences together with decoded dumps of their field values. Please note that sample sentences not accompanied by field dumps are not useful; I can get plenty of those.

Open-Source Implementations

The GPSD project ships an AIVDM/AIVDO sentence decoder as part of the daemon. This document was developed to be the specification for it, and it will decode all sentence type described herein.

The source-code repository of the GPSD project holds a conforming standalone Python decoder, ais.py, that is not included in shipped releases. It may be useful for developers working in that language.

[Schwehr] includes links to a collection of Python scripts for decoding and analyzing AIVDM sentences. Kurt Schwehr warns that this is research code rather than a production tool.

There is a GNU AIS project at SourceForge. It seems intended primarily to work directly with AIS radios.

The Maritec decoder looks to be pretty high-quality and can be exercised through a public web form. This is a useful resource for anyone qualifying an AIS decoder.

AIVDM/AIVDO Sentence Layer

AIVDM/AIVDO is a two-layer protocol. The outer layer is a variant of NMEA 0183, the ancient standard for data interchange in marine navigation systems; NMEA 0183 is described at [NMEA].

Here is a typical AIVDM data packet:

!AIVDM,1,1,,B,177KQJ5000G?tO`K>RA1wUbN0TKH,0*5C

And here is what the fields mean:

Field 1, !AIVDM, identifies this as an AIVDM packet.

Field 2 (1 in this example) is the count of fragments in the currently accumulating message. The payload size of each sentence is limited by NMEA 0183’s 82-character maximum, so it is sometimes required to split a payload over several fragment sentences.

Field 3 (1 in this example) is the fragment number of this sentence. It will be one-based. A sentence with a fragment count of 1 and a fragment number of 1 is complete in itself.

Field 4 (empty in this example) is a sequential message ID for multi-sentence messages.

Field 5 (B in this example) is a radio channel code. AIS uses the high side of the duplex from two VHF radio channels: AIS Channel A is 161.975Mhz (87B); AIS Channel B is 162.025Mhz (88B). In the wild, channel codes '1' and '2' may also be encountered; the standards do not prescribe an interpretation of these but it’s obvious enough.

Field 6 (177KQJ5000G?tO`K>RA1wUbN0TKH in this example) is the data payload. We’ll describe how to decode this in later sections.

Field 7 (0) is the number of fill bits requires to pad the data payload to a 6 bit boundary, ranging from 0 to 5. Equivalently, subtracting 5 from this tells how many least significant bits of the last 6-bit nibble in the data payload should be ignored. Note that this pad byte has a tricky interaction with the [ITU1371] requirement for byte alignment in over-the-air AIS messages; see the detailed discussion of message lengths and alignment in a later section.

The *-separated suffix (\*5C) is the NMEA 0183 data-integrity checksum for the sentence, preceded by "*". It is computed on the entire sentence including the AIVDM tag but excluding the leading "!".

For comparison, here is an example of a multi fragment sentence with a nonempty message ID field:

!AIVDM,2,1,3,B,55P5TL01VIaAL@7WKO@mBplU@<PDhh000000001S;AJ::4A80?4i@E53,0*3E
!AIVDM,2,2,3,B,1@0000000000000,2*55

Technically, NMEA0183 does not actually require that a !-led sentence be AIS. This format can be used for any encapsulated data. The syntax and semantics of fields 1-4 are fixed, and the fill-bit field and NMEA checksum are required, but the payload fields may contain any encapsulated data.

It is, however, a safe bet that any such sentence containing an A or B channel code in field 5 is AIVDM/AIVDO.

Talker IDS

The AI prefix commonly found on these sentences is an NMEA talker ID for a mobile AIS station. Other possible values are as listed:

Table 1. AIS talker IDs

!AB

NMEA 4.0 Base AIS station

!AD

NMEA 4.0 Dependent AIS Base Station

!AI

Mobile AIS station

!AN

NMEA 4.0 Aid to Navigation AIS station

!AR

NMEA 4.0 AIS Receiving Station

!AS

NMEA 4.0 Limited Base Station

!AT

NMEA 4.0 AIS Transmitting Station

!AX

NMEA 4.0 Repeater AIS station

!BS

Base AIS station (deprecated in NMEA 4.0)

!SA

NMEA 4.0 Physical Shore AIS Station

AIVDM/AIVDO Payload Armoring

The data payload is an ASCII-encoded bit vector. Each character represents six bits of data. To recover the six bits, subtract 48 from the ASCII character value; if the result is greater than 40 subtract 8. According to [IEC-PAS], the valid ASCII characters for this encoding begin with "0" (64) and end with "w" (87); however, the intermediate range "X" (88) to "\_" (95) is not used.

Table 2. ASCII payload armoring
Char ASCII Decimal Bits

"0"

48

0

000000

"1"

49

1

000001

"2"

50

2

000010

"3"

51

3

000011

"4"

52

4

000100

"5"

53

5

000101

"6"

54

6

000110

"7"

55

7

000111

"8"

56

8

001000

"9"

57

9

001001

":"

58

10

001010

";"

59

11

001011

"<"

60

12

001100

"="

61

13

001101

">"

62

14

001110

"?"

63

15

001111

"@"

64

16

010000

"A"

65

17

010001

"B"

66

18

010010

"C"

67

19

010011

"D"

68

20

010100

"E"

69

21

010101

"F"

70

22

010110

"G"

71

23

010111

"H"

72

24

011000

"I"

73

25

011001

"J"

74

26

011010

"K"

75

27

011011

"L"

76

28

011100

"M"

77

29

011101

"N"

78

30

011110

"O"

79

31

011111

"P"

80

32

100000

"Q"

81

33

100001

"R"

82

34

100010

"S"

83

35

100011

"T"

84

36

100100

"U"

85

37

100101

"V"

86

38

100110

"W"

87

39

100111

"`"

96

40

101000

"a"

97

41

101001

"b"

98

42

101010

"c"

99

43

101011

"d"

100

44

101100

"e"

101

45

101101

"f"

102

46

101110

"g"

103

47

101111

"h"

104

48

110000

"i"

105

49

110001

"j"

106

50

110010

"k"

107

51

110011

"l"

108

52

110100

"m"

109

53

110101

"n"

110

54

110110

"o"

111

55

110111

"p"

112

56

111000

"q"

113

57

111001

"r"

114

58

111010

"s"

115

59

111011

"t"

116

60

111100

"u"

117

61

111101

"v"

118

62

111110

"w"

119

63

111111

Concatenate all six-bit quantities found in the payload, MSB first. This is the binary payload of the sentence.

AIS Payload Data Types

Data in AIS message payloads (what you get after undoing the AIVDM/AIVDO armoring) is encoded as bit fields in the sentence. Bit fields may be interpreted in one of the following ways:

  • Signed or unsigned integer

  • Float (scaled from signed integer)

  • Flag or Boolean

  • Index into a controlled vocabulary

  • Reserved bits

  • Spare bits

  • Strings

Numeric bit fields are interpreted as big-endian twos-complement integers; when signed, the sign bit is the highest.

Float fields have an associated divisor which should be applied to convert to the correct units. In one case, the ROT field in message types 1-3, the scaling operation involves a more elaborate formula.

Flags are encoded as 1 for true/yes/on, 0 for false/no/off.

Indices into controlled vocabularies are numeric bit fields which must be interpreted using per-field string lists specified in the standards.

Spare fields generally seem to have been inserted in order to put certain field starts on 8-bit boundaries, and should be ignored. Decoders should not, however, assume that spare fields will be all zeroes.

Reserved fields should not be ignored, as they may be assigned for extension data in minor revisions of the AIS standard; it is noted in the message descriptions where this has already occurred. It is good practice for a decoder to make reserved fields available to client applications as uninterpreted bit fields.

Character-string fields within AIS messages are encoded in a special way, referred to as "six-bit" in the tables below. First, chop the string field into consecutive six-bit nibbles without padding (each span of three 8-bit bytes includes 4 of these). Each six-bit nibble maps to an ASCII character. Nibbles 0-31 map to the characters "@" ( ASCII 64) through "\_" (ASCII 95) respectively; nibbles 32-63 map to characters " " (ASCII 32) though "?" (ASCII 63). Lowercase ASCII letters, the backtick, right and left curly brackets, pipe bar, tilde and DEL cannot be encoded.

Table 3. Sixbit ASCII

000000

0

"@"

010000

16

"P"

100000

32

" "

110000

48

"0"

000001

1

"A"

010001

17

"Q"

100001

33

"!"

110001

49

"1"

000010

2

"B"

010010

18

"R"

100010

34

"""

110010

50

"2"

000011

3

"C"

010011

19

"S"

100011

35

"\#"

110011

51

"3"

000100

4

"D"

010100

20

"T"

100100

36

"$"

110100

52

"4"

000101

5

"E"

010101

21

"U"

100101

37

"%"

110101

53

"5"

000110

6

"F"

010110

22

"V"

100110

38

"&"

110110

54

"6"

000111

7

"G"

010111

23

"W"

100111

39

"\'"

110111

55

"7"

001000

8

"H"

011000

24

"X"

101000

40

"("

111000

56

"8"

001001

9

"I"

011001

25

"Y"

101001

41

")"

111001

56

"9"

001010

10

"J"

011010

26

"Z"

101010

42

"\*"

111010

58

":"

001011

11

"K"

011011

27

"["

101011

43

"\+"

111011

59

";"

001100

12

"L"

011100

28

"\"

101100

44

","

111100

60

"<"

001101

13

"M"

011101

29

"]"

101101

45

"-"

111101

61

"="

001110

14

"N"

011110

30

"\^"

101110

46

"."

111110

62

">"

001111

15

"O"

011111

31

"\_"

101111

47

"/"

111111

63

"?"

According to the standard, trailing unused characters in six-bit fields will be represented by "@" (six-bit zero); however, real-world encoders are not careful about this and often have nonzero garbage after the "@". The terminating "@" should not be considered part of the text, and any non-"@" characters after it should be discarded. It is also common to space-fill short fields such as ship and station name, so a decoder should strip trailing spaces after stripping at-signs and the garbage after them.

Trailing string fields are often specified as "up to" a certain number of bits. Decoders should be prepared to handle any field length up to that number, including zero.

AIS Payload Interpretation

The following table describes message types that are international standards from [ITU1371] and its revisions. There are also local and regional extensions used on inland waterways such as the Danube and the Thames and in British and Irish coastal waters; pointers to some of these are included later in this document.

Note that many sources use 1-origin numbering for the bits. We’ll use 0-origin in this document.

The first 6 bits of the payload (0-5) are the message type. Message types are as follows:

Table 4. Message types

01

Position Report Class A

02

Position Report Class A (Assigned schedule)

03

Position Report Class A (Response to interrogation)

04

Base Station Report

05

Static and Voyage Related Data

06

Binary Addressed Message

07

Binary Acknowledge

08

Binary Broadcast Message

09

Standard SAR Aircraft Position Report

10

UTC and Date Inquiry

11

UTC and Date Response

12

Addressed Safety Related Message

13

Safety Related Acknowledgement

14

Safety Related Broadcast Message

15

Interrogation

16

Assignment Mode Command

17

DGNSS Binary Broadcast Message

18

Standard Class B CS Position Report

19

Extended Class B Equipment Position Report

20

Data Link Management

21

Aid-to-Navigation Report

22

Channel Management

23

Group Assignment Command

24

Static Data Report

25

Single Slot Binary Message,

26

Multiple Slot Binary Message With Communications State

27

Position Report For Long-Range Applications

In normal operation, an AIS transceiver will broadcast a position report (type 1, 2, or 3) every 2 to 10 seconds depending on the vessel’s speed while underway, and every 3 minutes while the vessel is at anchor and stationary. It will send a type 5 identification every 6 minutes. (More detail is at [IALA], part 2.3)

Class 6 is used for unencrypted structured extension messages systems conforming to the Inland AIS standard defined by [INLAND], and by local authorities such as the St. Lawrence Seaway and the U.S Coast Guard’s PAWSS. This document describes all of the Class 6 special message formats approved for use in [IMO236], [IMO289], and [INLAND].

Class 8 is in common use for private encrypted messages, such as location transmission in military exercises. It is also used for unencrypted structured extension messages by Inland AIS, and by local authorities such as the St. Lawrence Seaway and PAWSS. This document describes all of the Class 8 special message formats approved for use in [IMO236], [IMO289], and [INLAND].

Classes 12 and 14 are used for text messaging, nominally safety-related but also for traffic control and occasionally chatter.

In practice, message types other than 1, 3, 4, 5, 18, and 24 are unusual or rare; many AIS transmitters never emit them.

An MMSI is a Mobile Marine Service Identifier, a unique 9-digit ID for the ship’s radio(s). The first three digits convey information about the country in which the ID was issued [ITU-MID]. US vessels traveling solely in U.S. waters sometimes incorrectly omit the leading "3", the geography code for North and Central America and Caribbean, emitting 8-digit MMSIs beginning with the U.S. country code of 669.

According to [MMSI], different formats of MMSI are used for different classes of transmitter. In the format descriptions below, a MID is a three-digit decimal literal ranging from 201 to 775 that identifies a country or other maritime jurisdiction. See [ITU-MID] for a list of MIDs.

Table 5. MID formats

8MIDXXXXX

Diver’s radio (not used in the U.S. in 2013)

MIDXXXXXX

Ship

0MIDXXXXX

Group of ships; the U.S. Coast Guard, for example, is 03699999

00MIDXXXX

Coastal stations

111MIDXXX

SAR (Search and Rescue) aircraft

99MIDXXXX

Aids to Navigation

98MIDXXXX

Auxiliary craft associated with a parent ship

970MIDXXX

AIS SART (Search and Rescue Transmitter)

972XXXXXX

MOB (Man Overboard) device

974XXXXXX

EPIRB (Emergency Position Indicating Radio Beacon) AIS

Detailed descriptions of message types 1-24 follow. Message types 1-22 are derived from [IALA]. Message type 23 was described to me by Mike Greene based on [IEC-62287]. Message type 24 was described to me by [Schwehr], whose Python toolkit decodes it. Message types 25-26 are reported by [Schwehr], who observes they were added in Version 3 of [ITU1371]. Message type 27 is direct from [ITU1371] version 4.

The "Member" column in these tables is not derived from any of the ITU standards or amendments. I have invented it in order to be able to describe a lossless textual encoding of AIS sentences in JSON. These names are also chosen for suitability as structure/object member names in computer languages, so that application programming interfaces across different languages can have a common and readily intelligible set to use.

The "T" column declares the data type of the field, and may have any of the values in the following table. It is intended to be used for generating bit field-extraction code directly from the message type descriptions.

u

Unsigned integer

U

Unsigned integer with scale - renders as float, suffix is decimal places

i

Signed integer

I

Signed integer with scale - renders as float, suffix is decimal places

b

Boolean

e

Enumerated type (controlled vocabulary)

x

Spare or reserved bit

t

String (packed six-bit ASCII)

d

Data (uninterpreted binary)

a

Array boundary, numeric suffix is maximum array size. ^ before suffix means preceding fields is the length. Following fields are repeated to end of message

The field breakdowns in this document have been checked against live decoded data rendered by known-good implementations for message types 1-15, 18-21, and 24. Described but unchecked are 16-17, 22-23, and 25-27. Also, the interpretation of IMO extension subtypes of messages 6 and 8 has yet to be tested.

Bit lengths and length ranges are given because decoders should check them against the message type. Messages with correct checksums but the wrong payload length for their type occur with about 0.3% frequency on AISHub; if you don’t reject these, your clients will see spurious zeros or garbage.

Types 1, 2 and 3: Position Report Class A

Type 1, 2 and 3 messages share a common reporting structure for navigational information; we’ll call it the Common Navigation Block (CNB). This is the information most likely to be of interest for decoding software. Total of 168 bits, occupying one AIVDM sentence. More information on the CNB is at [MSGS123]>.

Table 6. Common Navigation Block
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 1-3

6-7

2

Repeat Indicator

repeat

u

Message repeat count

8-37

30

MMSI

mmsi

u

9 decimal digits

38-41

4

Navigation Status

status

e

See "Navigation Status"

42-49

8

Rate of Turn (ROT)

turn

I3

See below

50-59

10

Speed Over Ground (SOG)

speed

U1

See below

60-60

1

Position Accuracy

accuracy

b

See below

61-88

28

Longitude

lon

I4

Minutes/10000 (see below)

89-115

27

Latitude

lat

I4

Minutes/10000 (see below)

116-127

12

Course Over Ground (COG)

course

U1

Relative to true north, to 0.1 degree precision

128-136

9

True Heading (HDG)

heading

u

0 to 359 degrees, 511 = not available.

137-142

6

Time Stamp

second

u

Second of UTC timestamp

143-144

2

Maneuver Indicator

maneuver

e

See "Maneuver Indicator"

145-147

3

Spare

x

Not used

148-148

1

RAIM flag

raim

b

See below

149-167

19

Radio status

radio

u

See below

The Repeat Indicator is a directive to an AIS transceiver that this message should be rebroadcast. This was intended as a way of getting AIS messages around hills and other obstructions in coastal waters, but is little used as base station coverage is more effective. It is intended that the bit be incremented on each retransmission, to a maximum of three hops. A value of 3 indicates "Do not repeat".

Table 7. Navigation Status

0

Under way using engine

1

At anchor

2

Not under command

3

Restricted manoeuverability

4

Constrained by her draught

5

Moored

6

Aground

7

Engaged in Fishing

8

Under way sailing

9

Reserved for future amendment of Navigational Status for HSC

10

Reserved for future amendment of Navigational Status for WIG

11

Power-driven vessel towing astern (regional use)

12

Power-driven vessel pushing ahead or towing alongside (regional use).

13

Reserved for future use

14

AIS-SART is active

15

Ubdefined (default)

Note, the AIS-SART value was added after [IALA] and designates an AIS transmitter in an survival craft such as a lifeboat. See [MSGS123] for the field specification and [SART] for background.

Turn rate is encoded as follows:

  • 0 = not turning

  • 1…​126 = turning right at up to 708 degrees per minute or higher

  • 1…​-126 = turning left at up to 708 degrees per minute or higher

  • 127 = turning right at more than 5deg/30s (No TI available)

  • -127 = turning left at more than 5deg/30s (No TI available)

  • 128 (80 hex) indicates no turn information available (default)

Values between 0 and 708 degrees/min coded by ROTAIS=4.733 * SQRT(ROTsensor) degrees/min where ROTsensor is the Rate of Turn as input by an external Rate of Turn Indicator. ROTAIS is rounded to the nearest integer value. Thus, to decode the field value, divide by 4.733 and then square it. Sign of the field value should be preserved when squaring it, otherwise the left/right indication will be lost.

Speed over ground is in 0.1-knot resolution from 0 to 102 knots. Value 1023 indicates speed is not available, value 1022 indicates 102.2 knots or higher.

The position accuracy flag indicates the accuracy of the fix. A value of 1 indicates a DGPS-quality fix with an accuracy of < 10ms. 0, the default, indicates an unaugmented GNSS fix with accuracy > 10m.

Longitude is given in in 1/10000 min; divide by 600000.0 to obtain degrees. Values up to plus or minus 180 degrees, East = positive, West \= negative. A value of 181 degrees (0x6791AC0 hex) indicates that longitude is not available and is the default.

Latitude is given in in 1/10000 min; divide by 600000.0 to obtain degrees. Values up to plus or minus 90 degrees, North = positive, South = negative. A value of 91 degrees (0x3412140 hex) indicates latitude is not available and is the default.

Course over ground will be 3600 (0xE10) if that data is not available.

Seconds in UTC timestamp should be 0-59, except for these special values:

  • 60 if time stamp is not available (default)

  • 61 if positioning system is in manual input mode

  • 62 if Electronic Position Fixing System operates in estimated (dead reckoning) mode,

  • 63 if the positioning system is inoperative.

The Regional Reserved field is intended for use by local maritime authorities. It is not known to be in any actual use up to 2009.

The Maneuver Indicator (143-144) may have these values:

Table 8. Maneuver Indicator

0

Not available (default)

1

No special maneuver

2

Special maneuver (such as regional passing arrangement)

Riverine and inland navigation systems conforming to [INLAND] designate this field "Blue Sign" with the following enumerated values:

Table 9. Blue Sign

0

Not available (default)

1

No

2

Yes

The interpretation of bits 143-147 has been a bit unstable. In [IALA] and therefore in the original [ITU1371], they were described like this:

Field Len Description

143-145

3

Regional Reserved

146-147

2

Spare

The interpretation of 143-144 as a special maneuver field is new in revision 3 of [ITU1371].

The RAIM flag indicates whether Receiver Autonomous Integrity Monitoring is being used to check the performance of the EPFD. 0 = RAIM not in use (default), 1 = RAIM in use. See [RAIM] for a detailed description of this flag.

Bits 149-167 are diagnostic information for the radio system. Consult [IALA] for detailed description of the latter.

Type 4: Base Station Report

This message is to be used by fixed-location base stations to periodically report a position and time reference. Total of 168 bits, occupying one AIVDM sentence.

The standard uses "EPFD" to designate any Electronic Position Fixing Device.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 4

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

MMSI

mmsi

u

9 decimal digits

38-51

14

Year (UTC)

year

u

UTC, 1-9999, 0 = N/A (default)

52-55

4

Month (UTC)

month

u

1-12; 0 = N/A (default)

56-60

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

61-65

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

66-71

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

72-77

6

Second (UTC)

second

u

0-59; 60 = N/A (default)

78-78

1

Fix quality

accuracy

b

As in Common Navigation Block

79-106

28

Longitude

lon

I4

As in Common Navigation Block

107-133

27

Latitude

lat

I4

As in Common Navigation Block

134-137

4

Type of EPFD

epfd

e

See "EPFD Fix Types"

138-147

10

Spare

x

Not used

148-148

1

RAIM flag

raim

b

As for common navigation block

149-167

19

SOTDMA state

radio

u

As in same bits for Type 1
Table 10. EPFD Fix Types
Code Position Fix Type

0

Undefined (default)

1

GPS

2

GLONASS

3

Combined GPS/GLONASS

4

Loran-C

5

Chayka

6

Integrated navigation system

7

Surveyed

8

Galileo

9

Reserved

10

Reserved

11

Reserved

11

Reserved

13

Reserved

14

Reserved

15

Internal GNSS

Note: though values 9-15 are marked "not used" in [IALA]. Decoders should be prepared to accept them as they are seen in the wild. [ITU1371] specifies type value 15 (all field bits 1) as "Internal GNSS".

Type 5: Static and Voyage Related Data

Message has a total of 424 bits, occupying two AIVDM sentences.

In practice, the information in these fields (especially ETA and destination) is not reliable, as it has to be hand-updated by humans rather than gathered automatically from sensors.

Also note that it is fairly common in the wild for this message to have a wrong bit length (420 or 422). Robust decoders should ignore trailing garbage and deal gracefully with a slightly truncated destination field.

Field Len Description Member/Type T Encoding

0-5

6

Message Type

type

u

Constant: 5

6-7

2

Repeat Indicator

repeat

u

Message repeat count

8-37

30

MMSI

mmsi

u

9 digits

38-39

2

AIS Version

ais_version

u

0=[ITU1371], 1-3 = future editions

40-69

30

IMO Number

imo

u

IMO ship ID number

70-111

42

Call Sign

callsign

t

7 six-bit characters

112-231

120

Vessel Name

shipname

t

20 six-bit characters

232-239

8

Ship Type

shiptype

e

See "Codes for Ship Type"

240-248

9

Dimension to Bow

to_bow

u

Meters

249-257

9

Dimension to Stern

to_stern

u

Meters

258-263

6

Dimension to Port

to_port

u

Meters

264-269

6

Dimension to Starboard

to_starboard

u

Meters

270-273

4

Position Fix Type

epfd

e

See "EPFD Fix Types"

274-277

4

ETA month (UTC)

month

u

1-12, 0=N/A (default)

278-282

5

ETA day (UTC)

day

u

1-31, 0=N/A (default)

283-287

5

ETA hour (UTC)

hour

u

0-23, 24=N/A (default)

288-293

6

ETA minute (UTC)

minute

u

0-59, 60=N/A (default)

294-301

8

Draught

draught

U1

Meters/10

302-421

120

Destination

destination

t

20 6-bit characters

422-422

1

DTE

dte

b

0=Data terminal ready, 1=Not ready (default).

423-423

1

Spare

x

Not used

[INLAND] specifies the following:

  • the IMO Number field should be zeroed for inland vessels.

  • ATIS code should be used for inland vessels

  • ship dimensions should be set to the maximum rectangle size of the convoy

  • draught information should be rounded up to nearest decimeter

  • For the destination, UN/LOCODE and ERI terminal codes should be used

Ship dimensions will be 0 if not available. For the dimensions to bow and stern, the special value 511 indicates 511 meters or greater; for the dimensions to port and starboard, the special value 63 indicates 63 meters or greater.

Table 11. Codes for Ship Type
Code Ship & Cargo Classification

0

Not available (default)

1-19

Reserved for future use

20

Wing in ground (WIG), all ships of this type

21

Wing in ground (WIG), Hazardous category A

22

Wing in ground (WIG), Hazardous category B

23

Wing in ground (WIG), Hazardous category C

24

Wing in ground (WIG), Hazardous category D

25

Wing in ground (WIG), Reserved for future use

26

Wing in ground (WIG), Reserved for future use

27

Wing in ground (WIG), Reserved for future use

28

Wing in ground (WIG), Reserved for future use

29

Wing in ground (WIG), Reserved for future use

30

Fishing

31

Towing

32

Towing: length exceeds 200m or breadth exceeds 25m

33

Dredging or underwater ops

34

Diving ops

35

Military ops

36

Sailing

37

Pleasure Craft

38

Reserved

39

Reserved

40

High speed craft (HSC), all ships of this type

41

High speed craft (HSC), Hazardous category A

42

High speed craft (HSC), Hazardous category B

43

High speed craft (HSC), Hazardous category C

44

High speed craft (HSC), Hazardous category D

45

High speed craft (HSC), Reserved for future use

46

High speed craft (HSC), Reserved for future use

47

High speed craft (HSC), Reserved for future use

48

High speed craft (HSC), Reserved for future use

49

High speed craft (HSC), No additional information

50

Pilot Vessel

51

Search and Rescue vessel

52

Tug

53

Port Tender

54

Anti-pollution equipment

55

Law Enforcement

56

Spare - Local Vessel

57

Spare - Local Vessel

58

Medical Transport

59

Noncombatant ship according to RR Resolution No. 18

60

Passenger, all ships of this type

61

Passenger, Hazardous category A

62

Passenger, Hazardous category B

63

Passenger, Hazardous category C

64

Passenger, Hazardous category D

65

Passenger, Reserved for future use

66

Passenger, Reserved for future use

67

Passenger, Reserved for future use

68

Passenger, Reserved for future use

69

Passenger, No additional information

70

Cargo, all ships of this type

71

Cargo, Hazardous category A

72

Cargo, Hazardous category B

73

Cargo, Hazardous category C

74

Cargo, Hazardous category D

75

Cargo, Reserved for future use

76

Cargo, Reserved for future use

77

Cargo, Reserved for future use

78

Cargo, Reserved for future use

79

Cargo, No additional information

80

Tanker, all ships of this type

81

Tanker, Hazardous category A

82

Tanker, Hazardous category B

83

Tanker, Hazardous category C

84

Tanker, Hazardous category D

85

Tanker, Reserved for future use

86

Tanker, Reserved for future use

87

Tanker, Reserved for future use

88

Tanker, Reserved for future use

89

Tanker, No additional information

90

Other Type, all ships of this type

91

Other Type, Hazardous category A

92

Other Type, Hazardous category B

93

Other Type, Hazardous category C

94

Other Type, Hazardous category D

95

Other Type, Reserved for future use

96

Other Type, Reserved for future use

97

Other Type, Reserved for future use

98

Other Type, Reserved for future use

99

Other Type, no additional information

Note that garbage values greater than 99 are supposed to be unused, but are not uncommon in the wild; AIS transmitters seem prone to put junk in this field when it’s not explicitly set. Decoders should treat these like value 0 rather than throwing an exception until and unless the controlled vocabulary is extended to include the unknown values.

Type 6: Binary Addressed Message

Message type 6 is an addressed point-to-point message with unspecified binary payload. The St. Lawrence Seaway AIS system, the USG PAWSS system, and the Port Authority of London use this payload for local extension messages. [IMO236] and [IMO289] describe payload use as international extension messages. This type is variable in length up to a maximum of 1008 bits (up to 5 AIVDM sentence payloads).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70

1

Retransmit flag

retransmit

b

0 = no retransmit (default) 1 = retransmitted

71

1

Spare

x

Not used

72-81

10

Designated Area Code

dac

u

Unsigned integer

82-87

6

Functional ID

fid

u

Unsigned integer

88

920

Data

data

d

Binary data May be shorter than 920 bits.

Interpretation of the binary payload is controlled by:

  • The Designated Area Code, which is a jurisdiction code: 366 for the United States. It uses the same encoding as the area designator in MMMSIs; see [ITU-MID]. 1 designates international (ITU) messages.

  • The FID, which is the Functional ID for a message subtype. In some sources this is abbreviated FI.

The following is a non-exhaustive list of standardized DAC-FID pairs in use for type 6. For an up-to-date list of registered application-specific messages, see [IALA-ASM].

DAC

FID

Source

Status

Description

1

12

[IMO236]

Deprecated

Dangerous cargo indication

1

14

[IMO236]

Deprecated

Tidal window

1

16

[IMO236]

Deprecated/In Use

Number of persons on board

1

16

[IMO289]

Standard

Number of persons on board

1

18

[IMO289]

Standard

Clearance time to enter port

1

20

[IMO289]

Standard

Berthing data (addressed)

1

23

[IMO289]

In use

Area notice (addressed)

1

25

[IMO289]

Standard

Dangerous Cargo indication

1

28

[IMO289]

Standard

Route info addressed

1

30

[IMO289]

Standard

Text description addressed

1

32

[IMO289]

Standard

Tidal Window

200

21

[INLAND]

Standard

ETA at lock/bridge/terminal

200

22

[INLAND]

Standard

RTA at lock/bridge/terminal

200

55

[INLAND]

Standard

Number of persons on board

235

10

[IALA-A126]

In use

AtoN monitoring data (UK)

250

10

[IALA-A126]

In use

AtoN monitoring data (ROI)

DAC/FID pairs are assigned separately per message type.

Note that the apparent presence of one of these DAC/FID pairs does not guarantee that the message is structured. Decoders should perform range validation on the structured fields and interpret the message as unstructured if any check fails. (As of Aug 2014 no such collisions have been in the wild; but see the parallel note for Type 8.)

A list of binary layouts for selected subtypes of message 6 follows.

IMO236 Dangerous Cargo Indication

This message should be used as a response to a request for Dangerous Cargo Indication from a competent authority. The message content is used to identify the port where the documents for the dangerous goods cargo can be found, e. g. last and next port of call, and to allow the requesting authority to form a danger estimate.

A message 6 subtype. DAC = 001 FID = 12. Fixed length: 360 bits. This is the [IMO236] version, now deprecated; there is a later [IMO289] version.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 12

88-117

30

Last Port Of Call

lastport

t

5 6-bit characters, UN locode

118-121

4

ETA month (UTC)

lmonth

u

1-12, 0=N/A (default)

122-126

5

ETA day (UTC)

lday

u

1-31, 0=N/A (default)

127-131

5

ETA hour (UTC)

lhour

u

0-23, 24=N/A (default)

132-137

6

ETA minute (UTC)

lminute

u

0-59, 60=N/A (default)

138-167

30

Next Port Of Call

nextport

t

5 6-bit characters, UN locode

168-171

4

ETA month (UTC)

nmonth

u

1-12, 0=N/A (default)

172-176

5

ETA day (UTC)

nday

u

1-31, 0=N/A (default)

177-181

5

ETA hour (UTC)

nhour

u

0-23, 24=N/A (default)

182-187

6

ETA minute (UTC)

nminute

u

0-59, 60=N/A (default)

188-307

120

Main Dangerous Good

dangerous

t

20 6-bit characters

308-331

24

IMD Category

imdcat

t

4 6-bit characters

332-344

13

UN Number

unid

u

1-3363 UN Number

345-354

10

Amount of Cargo

amount

u

Unsigned integer

355-356

2

Unit of Quantity

unit

e

See "Cargo Unit Codes"

357-359

3

Spare

x

Not used
Table 12. Cargo Unit Codes
Code Unit

0

Not available (default)

1

kg

2

metric tons

3

metric kilotons

IMO236 Tidal Window

This message should be used by shore stations to inform vessels about tidal windows which allow a vessel the safe passage of a fairway. The message includes 1-3 predictions of current speed and current direction. Acknowledgment is required.

A message 6 subtype. DAC = 001 FID = 14. Variable length: 190-376 bits This is the [IMO236] version; there is an [IMO289] version with different widths for the latitude, longitude, and current-speed fields (also the order of lat/lon is swapped).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

See Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 14

88-91

4

Month

month

u

1-12; 0 = N/A (default)

92-96

5

Day

day

u

1-31; 0 = N/A (default)

97

tidals

a3

Tidal information array

0-26

27

Latitude

lat

I4

Unit = minutes * 0.0001, 91000 = N/A (default), N positive, S negative.

27-54

28

Longitude

lon

I4

Unit = minutes * 0.0001, 181000 = N/A (default), E positive, W negative.

55-59

5

From UTC Hour

from_hour

u

0-23, 24 = N/A (default)

60-65

6

From UTC Minute

from_min

u

0-59, 60 = N/A (default)

66-70

5

To UTC Hour

to_hour

u

0-23, 24 = N/A (default)

71-76

6

To UTC Minute

to_min

u

0-59, 60 = N/A (default)

77-85

9

Current Dir. Predicted

cdir

u

0-359 deg, 360-N/A (default)

86-92

7

Current Speed Predicted

cspeed

U1

0-126, units of 0.1 knots, 127 = N/A (default).

The group of fields from longitude on may repeat twice more to convey up to three points of tidal information.

IMO236 Number of persons on board

This message should be used by a ship to report the number of persons on board, e.g. on request by a competent authority. Acknowledgment required.

A message 6 subtype. DAC = 001 FID = 16.

[IMO236] describes a fixed-length, 72-bit message with this layout:

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 16

55-68

14

# persons on board

persons

u

Unsigned integer 0 = N/A (default) 8191 = >= 8191 persons.

69-71

3

Spare

x

Not used

OPEN-QUESTION: Note that though this is a message 6 subtype and described in [IMO236] with the attribute "addressed", there is no destination address. A strikeout in [IMO236] suggests that this was originally a subtype of 8. It would be good defensive implementation for a decoder to accept either. Bit length may be used to distinguish them.

[IMO289] describes a fixed-length, 136-bit message with this layout:

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted.

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 16

88-100

13

# persons on board

persons

u

Unsigned integer, 0 = N/A (default), 8191 = >= 8191 persons.

101-135

35

Spare

x

Not used

IMO289 Clearance Time To Enter Port

This message provides specific ships with information on the port to call and time to enter. It should be transmitted by an authority competent to grant use of the port.

A message 6 subtype. DAC = 001 FID = 18. Fixed length: 360 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted.

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 18

88-97

10

Message Linkage ID

linkage

u

Unsigned integer

98-101

4

Month (UTC)

month

u

1-12; 0 = N/A (default)

102-106

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

107-111

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

112-117

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

118-237

120

Name of Port & Berth

portname

t

20 6-bit characters

238-267

30

Destination

destination

t

5 6-bit characters

268-292

25

Longitude

lon

I3

Unit = minutes * 0.001, 181000 = N/A (default).

293-316

24

Latitude

lat

I3

Unit = minutes * 0.001, 91000 = N/A (default).

317-359

43

Spare

x

Not used

IMO289 Berthing Data (addressed)

This message provides information on the ship’s berth. If sent from a ship it is a berthing request; if it is transmitted by a competent authority it is a berthing assignment.

A message 6 subtype. DAC = 001 FID = 20. Fixed Length: 360 bits.

The 2-bit fields after "availability" describe services which may be available at the berth. They are valid only if this master availability bit is on.

Field Len Description Member/Type T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default) 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

AC = 001

82-87

6

FID

fid

u

ID = 20

88-97

10

Message Linkage ID

linkage

u

Unsigned integer

98-106

9

Berth length

berth_length

u

In 1m steps, 1-510m, 511 = >= 511m 0 = N/A (default).

107-114

8

Berth Water Depth

berth_depth

U1

0.1-25.4m in 0.1 steps 255 = >= 25.5m 0 = N/A (default)

115-117

3

Mooring Position

position

e

See "Mooring Position"

118-121

4

Month (UTC)

month

u

1-12; 0 = N/A (default)

122-126

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

127-131

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

132-137

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

138-138

1

Services Availability

availability

b

0 = services unknown (default) 1 = services known

139-140

2

Agent

agent

e

See "Service Status"

141-142

2

Bunker/fuel

fuel

e

See "Service Status"

143-144

2

Chandler

chandler

e

See "Service Status"

145-146

2

Stevedore

stevedore

e

See "Service Status"

147-148

2

Electrical

electrical

e

See "Service Status"

149-150

2

Potable water

water

e

See "Service Status"

151-152

2

Customs house

customs

e

See "Service Status"

153-154

2

Cartage

cartage

e

See "Service Status"

155-156

2

Crane(s)

crane

e

See "Service Status"

157-158

2

Lift(s)

lift

e

See "Service Status"

159-160

2

Medical facilities

medical

e

See "Service Status"

161-162

2

Navigation repair

navrepair

e

See "Service Status"

163-164

2

Provisions

provisions

e

See "Service Status"

165-166

2

Ship repair

shiprepair

e

See "Service Status"

167-168

2

Surveyor

surveyor

e

See "Service Status"

169-170

2

Steam

steam

e

See "Service Status"

171-172

2

Tugs

tugs

e

See "Service Status"

173-174

2

Waste disposal (solid)

solidwaste

e

See "Service Status"

175-176

2

Waste disposal (liquid)

liquidwaste

e

See "Service Status"

177-178

2

Waste disposal (hazardous)

hazardouswaste

e

See "Service Status"

179-180

2

Reserved ballast exchange

ballast

e

See "Service Status"

181-182

2

Additional services

additional

e

See "Service Status"

183-184

2

Regional reserved 1

regional1

e

See "Service Status"

185-186

2

Regional reserved 2

regional2

e

See "Service Status"

187-188

2

Reserved for future

future1

e

See "Service Status"

189-190

2

Reserved for future

future2

e

See "Service Status"

191-310

120

Name of Berth

berth_name

t

20 6-bit characters

311-335

25

Longitude

berth_lon

I3

Minutes * 0.001, 181000 = N/A (default)

336-359

24

Latitude

berth_lat

I3

Minutes * 0.001, 91000 = N/A (default)

The UTC timestamp refers to the time requested or granted for berthing.

The longitude and latitude refer to the center of the berth.

Table 13. Mooring Position
Code Position

0

Not available (default)

1

Port-side to

2

Starboard-side to

3

Mediterranean (end-on) mooring

4

Mooring buoy

5

Anchorage

6-7

Reserved for future use
Table 14. Service Status
Code Meaning

0

Not available or requested (default)

1

Service available

2

No data or unknown

3

Not to be used

IMO289 Area Notice (addressed)

This should be used to convey time- and location-dependent information about hazards to navigation. For information-lifetime restrictions and usage guidance, refer to [ITU1371].

A message 6 subtype. DAC = 001 FID = 23. 230 to 1013 bits. There is a related Message 8 subtype for broadcast use.

The message consists of a fixed-length header of 143 bits, followed by 1 to 10 sub-area indications which are fixed-length records 87 bits long. Here is the message header format:

Table 15. Area Notice (addressed) message header
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted.

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 23

88-97

10

Message Linkage ID

linkage

u

Unsigned integer

98-104

7

Notice Description

notice

e

See "Area Notice Description"

105-108

4

Month (UTC)

month

u

1-12; 0 = N/A (default)

109-113

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

114-118

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

119-124

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

125-142

18

Duration

duration

u

In minutes, 262143 = N/A (default), 0 = cancel this notice.

143-145

3

Subarea shape #1

subarea type

u

0-5 (see "Subarea Types")

146-229

84

Subarea payload #1

shape data

array

See "Subarea Payloads"

230-232

3

Subarea shape #2

subarea type

u

0-5 (see "Subarea Types")

233-316

84

Subarea payload #2

shape data

array

See "Subarea Payloads"

317-319

3

Subarea shape #3

subarea type

u

0-5 (see "Subarea Types")

320-403

84

Subarea payload #3

shape data

array

See "Subarea Payloads"

404-406

3

Subarea shape #4

subarea type

u

0-5 (see "Subarea Types")

407-490

84

Subarea payload #4

shape data

array

See "Subarea Payloads"

491-493

3

Subarea shape #5

subarea type

u

0-5 (see "Subarea Types")

494-577

84

Subarea payload #5

shape data

array

See "Subarea Payloads"

578-580

3

Subarea shape #6

subarea type

u

0-5 (see "Subarea Types")

581-664

84

Subarea payload #6

shape data

array

See "Subarea Payloads"

665-667

3

Subarea shape #7

subarea type

u

0-5 (see "Subarea Types")

668-751

84

Subarea payload #7

shape data

array

See "Subarea Payloads"

752-754

3

Subarea shape #8

subarea type

u

0-5 (see "Subarea Types")

755-838

84

Subarea payload #8

shape data

array

See "Subarea Payloads"

839-841

3

Subarea shape #9

subarea type

u

0-5 (see "Subarea Types")

842-925

84

Subarea payload #9

shape data

array

See "Subarea Payloads"

926-928

3

Subarea shape #10

subarea type

u

0-5 (see "Subarea Types")

929-1012

84

Subarea payload #10

shape data

array

See "Subarea Payloads"

The Message Linkage field is, as usual, for linking to a textual explanatory message sent with the same linkage ID. The standard says that in this context it has the semantics of being an identifier of or reference to an area.

Notice description types are as follows:

Table 16. Area Notice Description

0

Caution Area: Marine mammals habitat

1

Caution Area: Marine mammals in area - reduce speed

2

Caution Area: Marine mammals in area - stay clear

3

Caution Area: Marine mammals in area - report sightings

4

Caution Area: Protected habitat - reduce speed

5

Caution Area: Protected habitat - stay clear

6

Caution Area: Protected habitat - no fishing or anchoring

7

Caution Area: Derelicts (drifting objects)

8

Caution Area: Traffic congestion

9

Caution Area: Marine event

10

Caution Area: Divers down

11

Caution Area: Swim area

12

Caution Area: Dredge operations

13

Caution Area: Survey operations

14

Caution Area: Underwater operation

15

Caution Area: Seaplane operations

16

Caution Area: Fishery – nets in water

17

Caution Area: Cluster of fishing vessels

18

Caution Area: Fairway closed

19

Caution Area: Harbor closed

20

Caution Area: Risk (define in associated text field)

21

Caution Area: Underwater vehicle operation

22

(reserved for future use)

23

Environmental Caution Area: Storm front (line squall)

24

Environmental Caution Area: Hazardous sea ice

25

Environmental Caution Area: Storm warning (storm cell or line of storms)

26

Environmental Caution Area: High wind

27

Environmental Caution Area: High waves

28

Environmental Caution Area: Restricted visibility (fog, rain, etc.)

29

Environmental Caution Area: Strong currents

30

Environmental Caution Area: Heavy icing

31

(reserved for future use)

32

Restricted Area: Fishing prohibited

33

Restricted Area: No anchoring.

34

Restricted Area: Entry approval required prior to transit

35

Restricted Area: Entry prohibited

36

Restricted Area: Active military OPAREA

37

Restricted Area: Firing – danger area.

38

Restricted Area: Drifting Mines

39

(reserved for future use)

40

Anchorage Area: Anchorage open

41

Anchorage Area: Anchorage closed

42

Anchorage Area: Anchorage prohibited

43

Anchorage Area: Deep draft anchorage

44

Anchorage Area: Shallow draft anchorage

45

Anchorage Area: Vessel transfer operations

46

(reserved for future use)

47

(reserved for future use)

48

(reserved for future use)

49

(reserved for future use)

50

(reserved for future use)

51

(reserved for future use)

52

(reserved for future use)

53

(reserved for future use)

54

(reserved for future use)

55

(reserved for future use)

56

Security Alert - Level 1

57

Security Alert - Level 2

57

Security Alert - Level 3

59

(reserved for future use)

60

(reserved for future use)

61

(reserved for future use)

62

(reserved for future use)

63

(reserved for future use)

64

Distress Area: Vessel disabled and adrift

65

Distress Area: Vessel sinking

66

Distress Area: Vessel abandoning ship

67

Distress Area: Vessel requests medical assistance

68

Distress Area: Vessel flooding

69

Distress Area: Vessel fire/explosion

70

Distress Area: Vessel grounding

71

Distress Area: Vessel collision

72

Distress Area: Vessel listing/capsizing

73

Distress Area: Vessel under assault

74

Distress Area: Person overboard

75

Distress Area: SAR area

76

Distress Area: Pollution response area

77

(reserved for future use)

78

(reserved for future use)

79

(reserved for future use)

80

Instruction: Contact VTS at this point/juncture

81

Instruction: Contact Port Administration at this point/juncture

82

Instruction: Do not proceed beyond this point/juncture

83

Instruction: Await instructions prior to proceeding beyond this point/juncture

84

Proceed to this location – await instructions

85

Clearance granted – proceed to berth

86

(reserved for future use)

87

(reserved for future use)

88

Information: Pilot boarding position

89

Information: Icebreaker waiting area

90

Information: Places of refuge

91

Information: Position of icebreakers

92

Information: Location of response units

93

VTS active target

94

Rogue or suspicious vessel

95

Vessel requesting non-distress assistance

96

Chart Feature: Sunken vessel

97

Chart Feature: Submerged object

98

Chart Feature: Semi-submerged object

99

Chart Feature: Shoal area

100

Chart Feature: Shoal area due north

101

Chart Feature: Shoal area due east

102

Chart Feature: Shoal area due south

103

Chart Feature: Shoal area due west

104

Chart Feature: Channel obstruction

105

Chart Feature: Reduced vertical clearance

106

Chart Feature: Bridge closed

107

Chart Feature: Bridge partially open

108

Chart Feature: Bridge fully open

109

(reserved for future use)

110

(reserved for future use)

111

(reserved for future use)

112

Report from ship: Icing info

113

(reserved for future use)

114

Report from ship: Miscellaneous information – define in associated text field

115

(reserved for future use)

116

(reserved for future use)

117

(reserved for future use)

118

(reserved for future use)

119

(reserved for future use)

120

Route: Recommended route

121

Route: Alternative route

122

Route: Recommended route through ice

123

(reserved for future use)

124

(reserved for future use)

125

Other – Define in associated text field

126

Cancellation – cancel area as identified by Message Linkage ID

127

Undefined (default)

Subarea types are as follows:

0

Circle or point

1

Rectangle

2

Sector

3

Polyline

4

Polygon

5

Associated text

6-7

Reserved

Subarea payload layouts are as follows:

Table 17. Circle or Point
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 0

3-4

2

Scale factor

scale

u

Power of 10 for area dimensions; 10^0 = scale factor 1 (default)

5-29

25

Longitude

lon

I3

Longitude of center point, Unit = minutes * 0.001, 181000 = N/A (default).

30-53

24

Latitude

lat

I3

Latitude of center point, Unit = minutes * 0.001, 91000 = N/A (default).

54-56

3

Precision

precision

u

Decimal places of precision (defaults to 4)

57-68

12

Radius

radius

u

Radius of area 0 = point (default), else 1-4095 * 10^scale m

69-86

18

Spare

x

Not used
Table 18. Rectangle
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 1

3-4

2

Scale factor

scale

u

Power of 10 for area dimensions; 10^0 = scale factor 1 (default)

5-29

25

Longitude

lon

I3

Longitude of SW corner Unit = minutes * 0.001, 181000 = N/A (default).

30-53

24

Latitude

lat

I3

Latitude of SW corner Unit = minutes * 0.001, 91000 = N/A (default).

54-56

3

Precision

precision

u

Decimal places of precision (defaults to 4)

57-64

8

E dimension

east

u

Box dimension east 0 = N/S line (default), else 1-255 * 10^scale m

65-72

8

N dimension

north

u

Box dimension north 0 = E/W line (default), else 1-255 * 10^scale m

73-81

9

Orientation

orientation

u

Degrees clockwise from true N, 0 = no rotation (default), else 1-359, 360-511 reserved.

82-86

5

Spare

x

Not used
Table 19. Sector
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 2

3-4

2

Scale factor

scale

u

Power of 10 for area dimensions; 10^0 = scale factor 1 (default)

5-29

25

Longitude

lon

I3

Longitude of center point, Unit = minutes * 0.001, 181000 = N/A (default).

30-53

24

Latitude

lat

I3

Latitude of center point, Unit = minutes * 0.001, 91000 = N/A (default).

54-56

3

Precision

precision

u

Decimal places of precision (defaults to 4)

57-68

12

Radius

radius

u

Radius of area 0 = point (default), else 1-4095 * 10^scale m

69-77

9

Left boundary

left

u

Degrees clockwise from true N, 0 = no rotation (default), else 1-359, 360-511 reserved.

78-86

9

Right boundary

right

u

Degrees clockwise from true N, 0 = no rotation (default), else 1-359, 360-511 reserved.
Table 20. Polyline
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 3

3-4

2

Scale factor

scale

u

Power of 10 for area dimensions; 10^0 = scale factor 1 (default)

5

waypoints

a4

Waypoints array

0-9

10

Bearing

bearing

u

True bearing in half-degree steps from previous waypoint; 720 = N/A (default).

10-19

10

Distance

distance

u

Distance from prev. waypoint, 0 = no point (default), else 1-1023 * 10^scale m

The last two fields are repeated 4 times; the final 2 bits of 87 are unused. A polyline must be preceded by either (a) a circle, in which case the first bearing is from the center, or (b) a polyline, in which case the first bearing is from the implied last point.

Table 21. Polygon
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 4

3-4

2

Scale factor

scale

u

Power of 10 for area dimensions; 10^0 = scale factor 1 (default)

5

vertices

a4

Vertices array

0-9

10

Bearing

bearing

u

True bearing in half-degree steps from previous vertex; 720 = N/A (default).

10-19

10

Distance

distance

u

Distance from prev. vertex,

The last two fields are repeated 4 times; the final 2 bits of 87 are unused. A polygon must be preceded by a circle; the first bearing is from the circle center, which is treated as the zero vertex. There is an implied boundary from the last polygon vertex to the zero vertex.

Table 22. Associated text
Field Len Description Member/Type T Units

0-2

3

Shape of area

shape

e

Constant: 5

3-86

84

Text

text

t

14 chars of packed 6-bit.

IMO289 Dangerous Cargo Indication

See the IMO236 variant for the meaning of this message.

A message 6 subtype. DAC = 001 FID = 25. Variable length: 117-576 bits. This is the [IMO289] version; there is an earlier [IMO236] version with a different layout, deprecated in [IMO289].

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default) 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 25

88-89

2

Unit of Quantity

unit

e

See "Cargo Unit Codes"

90-99

10

Amount of Cargo

amount

u

Unsigned integer 0 = N/A (default) 0 = N/A (default)

100

cargos

a28

Cargo types array

0-3

4

Cargo code

code

e

See "Cargo Codes"

4-16

13

Cargo subtype

subtype

u

Unsigned integer 0 = N/A (default)

The last two fields may repeat to describe up to 28 subcargos. The count of repetitions must be computed from the message payload length.

For cargo unit codes, see the description of the IMO236 variant of this message.

Table 23. Cargo Codes
Code Code under which cargo is carried

0

Not available (default)

1

IMDG Code (in packed form)

2

IGC code

3

BC Code (from 1.1.2011 IMSBC)

4

MARPOL Annex I List of oils (Appendix 1)

5

MARPOL Annex II IBC Code

6

Regional use

7-15

Reserved for future use

The subtype field may be interpreted as an IMDG class or division code (if the cargotype is 1 = IMDG code) or as a UN number (if the cargotype is 2 = IGC code) or as a pair of BC class and IMDG class (if the cargotype is 3 = BC code) or as a MARPOL Annex I code (if the cargotype is 4 = MARPOL Annex I) or as a MARPOL Annex II code (if the cargotype is 5 = MARPOL Annex II).

Table 24. Dangerous Cargo Indication: MARPOL Annex I list of oils

0

N/A (default)

1

asphalt solutions

2

oils

3

distillates

4

gas oil

5

gasoline blending stocks

6

gasoline

7

jet fuels

8

naphtha

9-15

reserved for future use
Table 25. Dangerous Cargo Indication: MARPOL Annex II list of oils

0

N/A (default)

1

Category X

2

Category Y

3

Category Z

4

Other substances

5-7

reserved for future use

IMO289 Route Information (addressed)

The content of this message is a time and a list of waypoints describing a course. It has a broadcast equivalent that is a message 8 subtype.

A message 6 subtype. DAC = 001 FID = 28. Variable length: 204-1029 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmission (default), 1 = retransmitted.

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 28

88-97

10

Message Linkage ID

linkage

u

Unsigned integer

98-100

3

Sender Class

sender

u

0 = ship (default), 1 = authority, 27 = reserved for future use

101-105

5

Route Type

rtype

e

See "Route Type Codes"

106-109

4

Start month (UTC)

month

u

1-12, 0=N/A (default)

110-114

5

Start day (UTC)

day

u

1-31, 0=N/A (default)

115-119

5

Start hour (UTC)

hour

u

0-23, 24=N/A (default)

120-125

6

Start minute (UTC)

minute

u

0-59, 60=N/A (default)

126-143

18

Duration

duration

u

Minutes from start time, 0 = cancel route, 262,143 = N/A (default),

144-148

5

waycount

u

Waypoint count (1-16), Values 17-31 are not used.

149

waypoints

a^16

Waypoint array

0-27

28

Longitude

lon

I4

Minutes * 0.0001, 181000 = N/A (default), E positive, W negative.

28-54

27

Latitude

lat

I4

Minutes * 0.0001, 91000 = N/A (default), N positive, S negative.

The final pair of fields in the table above is a waypoint. The message may end with 1 to 16 waypoints.

Table 26. Route Type Codes

0

Undefined (default)

1

Mandatory

2

Recommended

3

Alternative

4

Recommended route through ice

5

Ship route plan

6-30

Reserved for future usage

31

Cancel route identified by message linkage

IMO289 Text description (addressed)

This message may be used to attach a text description to another message with a Message Linkage ID matching this one. It is intended that the combination of MMSI and Message Linkage ID should be unique.

A message 6 subtype. DAC = 001 FID = 30. Variable length: 104-1028 bits.

Intended to be used to associate a text annotation with another message via the Message Linkage ID field.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 30

88-97

10

Message Linkage ID

linkage

u

Unsigned integer

98-?

6-930

Description

description

t

String

There is an equivalent subtype of message 8 that is a broadcast description.

Tidal Window (IMO289)

See the [IMO289] version of this message for intended meaning.

A message 6 subtype. DAC = 001 FID = 32. Variable length: 186-362 bits. This is the [IMO289] version; there is an [IMO289] version with different bit widths for the latitude and longitude fields.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 001

82-87

6

FID

fid

u

FID = 32

88-91

4

Month

month

u

1-12; 0 = N/A (default)

92-96

5

Day

day

u

1-31; 0 = N/A (default)

97

tidals

a3

Tidal information array

0-24

25

Longitude

lon

I3

Unit = minutes * 0.001, 181000 = N/A (default), E positive, W negative.

25-48

24

Latitude

lat

I3

Unit = minutes * 0.001. 91000 = N/A (default), N positive, S negative.

49-53

5

From UTC Hour

from_hour

u

0-23, 24 = N/A (default)

54-59

6

From UTC Minute

from_min

u

0-59, 60 = N/A (default)

60-64

5

To UTC Hour

to_hour

u

0-23, 24 = N/A (default)

65-70

6

To UTC Minute

to_min

u

0-59, 60 = N/A (default)

71-79

9

Current Dir. Predicted

cdir

u

0-359 true bearing, 360 = N/A (default).

80-87

8

Current Speed Predicted

cspeed

U1

0-250, units of 0.1 knots, 251 = speed >= 25.1 knots, 255 = N/A (default).

The group of fields from longitude on may repeat twice more to convey up to three points of tidal information.

ETA at lock/bridge/terminal (Inland AIS)

A message 6 subtype. DAC = 200 FID = 21. Fixed length, 248 bits.

Should be used by inland vessels only, to send an ETA report to a lock, bridge or terminal in order to apply for a time slot in resource planning.

An acknowledgment by Inland AIS message 22 should be received within 15 minutes. Otherwise, the Inland AIS message 21 should be repeated once.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 200

82-87

6

FID

fid

u

FID = 21

88-99

12

UN Country Code

country

t

2 six-bit characters

100-117

18

UN/LOCODE

locode

t

3 six-bit characters

118-147

30

Fairway section

section

t

5 six-bit characters

148-177

30

Terminal code

terminal

t

5 six-bit characters

178-207

30

Fairway hectometre

hectometre

t

5 six-bit characters

208-211

4

ETA month

month

u

1-12, 0=N/A (default)

212-216

5

ETA day

day

u

1-31, 0=N/A (default)

217-221

5

ETA hour

hour

u

0-23, 24=N/A (default)

222-227

6

ETA minute

minute

u

0-59, 60=N/A (default)

228-230

3

Assisting Tugs

tugs

u

0-6, 7 = unknown (default)

231-242

12

Air Draught

airdraught

u

0-4000 * 0.01m, 0 = Unknown (default)

243-247

5

Spare

x

Not used

[INLAND] says of the Destination MMSI field "a virtual MMSI number should be used for each country, each national AIS network should route messages addressed to other countries using this virtual MMSI number".

OPEN-QUESTION: [INLAND] does not specify whether ETA time is UTC or local.

RTA at lock/bridge/terminal (Inland AIS)

A message 6 subtype. DAC = 200 FID = 22. Fixed length, 232 bits.

This message should be sent by base stations only, to assign a RTA at a lock, bridge or terminal to a certain vessel in response to the preceding ETA request.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 200

82-87

6

FID

fid

u

FID = 21

88-99

12

UN Country Code

country

t

2 six-bit characters

100-117

18

UN/LOCODE

locode

t

3 six-bit characters

118-147

30

Fairway section

section

t

5 six-bit characters

148-177

30

Terminal code

terminal

t

5 six-bit characters

178-207

30

Fairway hectometre

hectometre

t

5 six-bit characters

208-211

4

RTA month

month

u

1-12, 0=N/A (default)

212-216

5

RTA day

day

u

1-31, 0=N/A (default)

217-221

5

RTA hour

hour

u

0-23, 24=N/A (default)

222-227

6

RTA minute

minute

u

0-59, 60=N/A (default)

228-229

2

Status

status

e

See "Status Codes" below

230-231

2

Spare

x

Not used

OPEN-QUESTION: [INLAND] does not specify whether ETA time is UTC or local.

OPEN-QUESTION: No default is specified for the Status field.

Table 27. Lock/Bridge/Terminal status codes

0

Operational

1

Limited operation

2

Out of order

3

N/A

Number of persons on board (Inland AIS)

This message should be sent by inland vessels only, to inform about the number of persons (passengers, crew, and shipboard personnel) on board.

A message 6 subtype. DAC = 200 FID = 55. Fixed length, 168 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 200

82-87

6

FID

fid

u

FID = 55

88-95

8

# crew on board

crew

u

Unsigned integer 0-254, 255 = Unknown (default)

96-108

13

# passengers on board

passengers

u

Unsigned integer 0-8190, 8191 = Unknown (default)

109-116

8

# personnel on board

personnel

u

Unsigned integer 0-254, 255 = Unknown (default)

117-167

51

Spare

x

Not used

AtoN monitoring data (GLA)

This message provides AtoN (Aid to navigation) monitoring data for the General Lighthouse Authorities (GLA), which consists of Trinity House (England & Wales), Northern Lighthouse Board (Scotland) and the Commissioners of Irish Lights (Ireland). It is described in [IALA-A126].

A message 6 subtype. DAC = 235 or 250 FID = 10. Fixed length: 136 bits.

DAC and FI are user configurable, DAC=235/FI=10 is used in UK, DAC=250/FI=10 in the Republic Of Ireland.

The interval between the transmissions of these messages will be synchronized with message 21, although not necessarily at the same reporting rate. If Message 21 is not used at a particular site, then the reporting interval should be selected to minimize the power requirement of the transponder, whilst still providing enough data to enable meaningful diagnostic analysis.

OPEN-QUESTION: [INLAND] lists a broadcast (type 8) variant of this message, but without indicating how the Destination MMSI field is to be set or interpreted. Robust implementations should accept and process this variant.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-70

1

Retransmit flag

retransmit

u

0 = no retransmit (default), 1 = retransmitted

71-71

1

Spare

x

Not used

72-81

10

DAC

dac

u

DAC = 235 or 250

82-87

6

FID

fid

u

FID = 10

88-97

10

Analogue

ana_int

u

0.05-36V, 0.05V step Supply voltage to AIS Unit 0 = Not Used

98-107

10

Analogue (ext. #1)

ana_ext1

u

0.05-36V, 0.05V step 0 = Not Used

108-117

10

Analogue (ext. #2)

ana_ext2

u

0.05-36V, 0.05V step 0 = Not Used

118-119

2

RACON status

racon

u

00 = no RACON installed 01 = RACON not monitored 10 = RACON operational 11 = RACON ERROR

120-121

2

Light status

light

u

00 = no light or no monitoring 01 = Light ON 10 = Light OFF 11 = Light ERROR

122

1

Health

health

b

0 = Good Health, 1 = Alarm

123-130

8

Status (external)

stat_ext

u

7 Digital Input 0=Off, 1=On : : 0 Digital Input 0=Off, 1=On

131-131

1

Position status

off_pos

b

0=On position, 1=Off position

132-135

4

Spare

x

Not used

Type 7: Binary Acknowledge

Message type 7 is a receipt acknowledgment to the senders of a previous messages of type 6. Total length varies between 72 and 168 bits by 32-bit increments, depending on the number of destination MMSIs included.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 7

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-69

30

MMSI number 1

mmsi1

u

9 decimal digits

70-71

2

Sequence for MMSI 1

mmsiseq1

u

Not used

72-101

30

MMSI number 2

mmsi2

u

9 decimal digits

102-103

2

Sequence for MMSI 2

mmsiseq2

u

Not used

104-133

30

MMSI number 3

mmsi3

u

9 decimal digits

134-135

2

Sequence for MMSI 3

mmsiseq3

u

Not used

136-165

30

MMSI number 4

mmsi4

u

9 decimal digits

166-167

2

Sequence for MMSI 4

mmsiseq4

u

Not used

Use of the MMSI sequence fields was introduced in ITU-1371-5 to indicate the sequence number of the Type 6 to which this responds. In earlier versions these were spare fields.

Type 8: Binary Broadcast Message

Message type 8 is a broadcast message with unspecified binary payload. The St. Lawrence Seaway AIS system, the USG PAWSS system, and the Port Authority of London use this payload for local extension messages. [IMO236] and [IMO289] describe payload use as international extension messages. This type is variable in length up to a maximum of 1008 bits (up to 5 AIVDM sentence payloads).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

Designated Area Code

dac

u

Unsigned integer

50-55

6

Functional ID

fid

u

Unsigned integer

56

952

Data

data

d

Binary data, May be shorter than 952 bits.

Interpretation of the binary payload is controlled by DAC/FID as in message type 6. The following is a non-exhaustive list of standardized DAC-FID pairs in use for type 8; for an up-to-date list of registered application-specific messages, see [IALA-ASM]:

DAC FID Sub Source Status Description

1

11

[IMO236]

Deprecated/In Use

Meteorological/Hydrological Data

1

13

[IMO236]

Deprecated

Fairway closed

1

15

[IMO236]

Deprecated

Extended ship and voyage

1

17

[IMO289]

In use

VTS-Generated/Synthetic targets

1

19

[IMO289]

Standard

Marine traffic signals

1

21

[IMO289]

Standard

Weather observation from ship

1

22

[IMO289]

In use

Area notice (broadcast)

1

24

[IMO289]

Standard

Extended ship and voyage

1

26

[IMO289]

Standard

Environmental

1

27

[IMO289]

Standard

Route info broadcast

1

29

[IMO289]

Standard

Text description broadcast

1

31

[IMO289]

In use

Meteorological and Hydrological

200

10

[INLAND]

Standard

Ship static and voyage related data

200

23

[INLAND]

Standard

EMMA warning report

200

24

[INLAND]

Standard

Water levels

200

40

[INLAND]

Standard

Signal status

316/366

1

2

[SEAWAY]

In use

Wind

316/366

1

1

[SEAWAY]

In use

Weather station

316/366

1

3

[SEAWAY]

In use

Water level

316/366

1

6

[SEAWAY]

In use

Water flow

316/366

2

1

[SEAWAY]

In use

Lockage Order

316/366

2

2

[SEAWAY]

In use

Estimated Lock Times

316/366

32

1

[SEAWAY]

In use

Seaway Version Message

366

1

4

[SEAWAY]

In use

PAWS Hydro / Current

366

1

6

[SEAWAY]

In use

PAWS Hydro / Salinity Temp

366

1

3

[SEAWAY]

In use

PAWS Vessel Procession Order

DAC/FID pairs are assigned separately per message type. For St. Lawrence Seaway messages, the DAC may be 316 (Canada) or 366 (U.S.) depending on the transmitter location.

Note that the apparent presence of one of these DAC/FID pairs does not guarantee that the message is structured. Decoders should perform range validation on the structured fields and interpret the message as unstructured if any check fails. Actual false matches with DAC/FID = 200/10 have been observed in the wild.

DAC/FID pairs 1/23, 1/28, and 1/30 have addressed versions described under type 6.

FID types 11-15 are being phased out and are not to be used after 1 Jan 2013. The deprecated IMO236 1/11 has a different binary layout from the IMO289 1/31. FID type 17 is in use; there is a proposed update for it in [IMO289].

Breakdowns of Message 8 subtypes from [IMO289] follow.

Meteorological and Hydrological Data (IMO236)

A message 8 subtype. DAC = 001 FID = 11. Fixed length, 352 bits. This is in use and described in [IMO236], but has been deprecated by [IMO289] in favor of a message with the same title but FID = 31 and a different binary layout. [IMO236] specifies a maximum interval between broadcast of this message of 12 minutes.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 11

56-79

24

Latitude

lat

I3

Unit = minutes * 0.001, 0x7FFFFF = N/A (default), E positive, W negative.

80-104

25

Longitude

lon

I3

Unit = minutes * 0.001, 0xFFFFFF = N/A (default), N positive, S negative.

105-109

5

Day (UTC)

day

u

1-31, 31=N/A (default)

110-114

5

Hour (UTC)

hour

u

0-23, 31=N/A (default)

115-120

6

Minute (UTC)

minute

u

0-59, 63=N/A (default)

121-127

7

Average Wind Speed

wspeed

u

10-min avg wind speed, knots, 127 = N/A (default).

128-134

7

Gust Speed

wgust

u

10-min max wind speed, knots, 127 = N/A (default).

135-143

9

Wind Direction

wdir

u

0-359, degrees from true north 511 = N/A (default)

144-152

9

Wind Gust Direction

wgustdir

u

0-359, degrees from true north 511 = N/A (default)

153-163

11

Air Temperature

temperature

u

Dry bulb temp: 0.1 deg C -60.0 to +60.0, 2047 = N/A (default),

164-170

7

Relative Humidity

humidity

u

0-100%, units of 1%, 127 = N/A (default).

171-180

10

Dew Point

dewpoint

u

-20.0 to +50.0: 0.1 deg C, 1023 = N/A (default),

181-189

9

Air Pressure

pressure

u

800-1200hPa: units 1hPa, 511 = N/A (default).

190-191

2

Pressure Tendency

pressuretend

e

0 = steady, 1 = decreasing, 2 = increasing, 3 - N/A (default).

192-199

8

Horiz. Visibility

visibility

U1

0-25.0, units of 0.1nm 255 = N/A (default)

200-208

9

Water Level

waterlevel

I1

-10.0 to +30.0 in 0.1m, 511 = N/A (default).

209-210

2

Water Level Trend

leveltrend

e

0 = steady, 1 = decreasing, 2 = increasing, 3 - N/A (default).

211-218

8

Surface Current Speed

cspeed

U1

0.0-25.0 knots: units 0.1 knot

219-227

9

Surface Current Direction

cdir

u

0-359: deg from true north, 511 = N/A (default)

228-235

8

Current Speed #2

cspeed2

U1

0.0-25.0 in units of 0.1 knot, 255 = N/A (default).

236-244

9

Current Direction #2

cdir2

u

0-359: deg. fom true north, 511 = N/A (default)

245-249

5

Measurement Depth #2

cdepth2

U1

0-30m down: units 0.1m, 31 = N/A (default).

250-257

8

Current Speed #3

cspeed3

U1

0.0-25.0: units of 0.1 knot, 255 = N/A (default).

258-266

9

Current Direction #3

cdir3

u

0-359: degrees fom true north, 511 = N/A (default).

267-271

5

Measurement Depth #3

cdepth3

U1

0-30m down: units 0.1m, 31 = N/A (default).

272-279

8

Wave height

waveheight

U1

0-25m: units of 0.1m, 255 = N/A (default).

280-285

6

Wave period

waveperiod

u

Seconds 0-60: 63 = N/A (default).

286-294

9

Wave direction

wavedir

u

0-359: deg. ffom true north, 511 = N/A (default).

295-302

8

Swell height

swellheight

U1

0-25m: units of 0.1m 255 = N/A (default).

303-308

6

Swell period

swellperiod

u

Seconds 0-60: 63 = N/A (default).

309-317

9

Swell direction

swelldir

u

0-359: deg. fom true north, 511 = N/A (default).

318-321

4

Sea state

seastate

e

See "Beaufort Scale"

322-331

10

Water Temperature

watertemp

U1

-10.0 to 50.0: units 0.1 C, 1023 = N/A (default).

332-334

3

Precipitation

preciptype

e

See "Precipitation Types"

335-343

9

Salinity

salinity

U1

0.0-50.0%: units 0.1%, 511 = N/A (default)

344-345

2

Ice

ice

e

0 = No 1 = Yes 2 = (reserved for future use) 3 = not available = default

346-351

6

Spare

x

Not used

[IMO236] says "If there is no data available, default value to be transmitted is the highest available binary value for that particular data field.", the above table reflects that. The day, hour and minute have to be considered not available when all three are set to their individual "N/A" value. For the latitude and the longitude, the highest positive value is used, as the highest available binary value for a signed integer is -1, which would forbid the -0.001/-0.001 position. The replacement FID=31 message has different default values that remove any ambiguities.

[IMO236] gives the length of this message as 352, but lists only 336 payload bits.

Water level is deviation from local chart datum and includes tide.

The waveheight field is labeled as "Significant" in [IMO236], for whatever that means.

The seastate field has a note in [IMO236] reading "(manual input?)"?

WMO 306 Code table 4.201 specifies the following precipitation type values:

Table 28. Precipitation Types
Code Precipitation Type

0

Reserved

1

Rain

2

Thunderstorm

3

Freezing rain

4

Mixed/ice

5

Snow

6

Reserved

7

N/A (default)
Table 29. Beaufort Scale
Scale Description Sea Conditions

0

Calm

Flat.

1

Light air

Ripples without crests.

2

Light breeze

Small wavelets. Crests of glassy appearance, not breaking.

3

Gentle breeze

Large wavelets. Crests begin to break; scattered whitecaps.

4

Moderate breeze

Small waves.

5

Fresh breeze

Moderate (1.2 m) longer waves. Some foam and spray.

6

Strong breeze

Large waves with foam crests and some spray.

7

High wind

Sea heaps up and foam begins to streak.

8

Gale

Moderately high waves with breaking crests forming spindrift. Streaks of foam.

9

Strong gale

High waves (6-7 m) with dense foam. Wave crests start to roll over. Considerable spray.

10

Storm

Very high waves. The sea surface is white and there is considerable tumbling. Visibility is reduced.

11

Violent storm

Exceptionally high waves.

12

Hurricane force

Huge waves. Air filled with foam and spray. Sea completely white with driving spray. Visibility greatly reduced.

13

N/A (default)

14-15

Reserved

Fairway Closed

This message should be broadcast from shore stations to inform ships, in particular to give guidance to large vessels about temporary closed fairways or sections in ports.

A message 8 subtype. DAC = 001 FID = 13. Fixed length, 472 bits. Described in [IMO236] but deprecated by [IMO289].

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 13

56-175

120

Reason For Closing

reason

t

20 6-bit characters

176-295

120

Location Of Closing From

closefrom

t

20 6-bit characters

296-415

120

Location of Closing To

closeto

t

20 6-bit characters

416-425

10

Radius extension

radius

u

0-1000, 10001 = N/A (default)

426-427

2

Unit of extension

extunit

u

0=m, 1=km, 2=nm, 3=cables

428-432

5

From day (UTC)

fday

u

1-31, 0=N/A (default)

433-436

4

From month (UTC)

fmonth

u

1-12, 0=N/A (default)

437-441

5

From hour (UTC)

fhour

u

0-23, 24=N/A (default)

442-447

6

From minute (UTC)

fminute

u

0-59, 60=N/A (default)

448-452

5

To day (UTC)

tday

u

1-31, 0=N/A (default)

453-456

4

To month (UTC)

tmonth

u

1-12, 0=N/A (default)

457-461

5

To hour (UTC)

thour

u

0-23, 24=N/A (default)

462-467

6

To minute (UTC)

tminute

u

0-59, 60=N/A (default)

468-471

4

Spare

x

Not used

No default is specified for the radius field in the standard.

IMO236 Extended Ship Static and Voyage Related Data

This message should be used by a ship to report the height over keel.

A message 8 subtype. DAC = 001 FID = 15 in [IMO236]. Fixed length, 72 bits. Deprecated in [IMO289].

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 15

55-66

11

Air Draught

airdraught

u

Height in 0.1m steps 0 = N/A (default), 204.7 = >= 204.7 m,

67-71

5

Spare

x

Not used

VTS-Generated/Synthetic targets

A message 8 subtype. DAC = 001 FID = 17. Variable length: 176-536 bits. This message is laid out identically in [IMO236] and [IMO289]. In [IMO236] it is titled "Pseudo-AIS Targets".

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 17

56

targets

a4

Synthetic targets array

0-1

2

Identifier type

idtype

e

0 = id is the MMSI number, 1 = id is the IMO number, 2 = id is the call sign, 3 = Other (default).

2-43

42

Target identifier

id

u

Target ID data.

44-47

4

Spare

x

Not used

48-71

24

Latitude

lat

I3

Minutes * 0.001, 91000 = N/A (default), N positive, S negative.

72-96

25

Longitude

lon

I3

Minutes * 0.001, 181000 = N/A (default), E positive, W negative.

97-105

9

Course Over Ground

course

u

0-359 deg from true north, 360 = N/A (default).

106-111

6

Time Stamp

second

u

Second of UTC timestamp.

112-121

10

Speed Over Ground

speed

u

0-254 in knots, 255 = N/A.

The interpretation of the target identifier field depends on the preceding type key. For 0 and 1 it is a big-endian unsigned binary integer (as shown above). For type 2 and 3 it is 6-bit ASCII text. An unknown target is expressed by type 3 and the string "@@@@@@@".

OPEN-QUESTION: [IMO289] says: "When MMSI or IMO number is used, the least significant bit should equal bit zero of the Target Identifier." It is unclear how "bit zero" is to be interpreted, but it is not possible to reconcile interpreting it as the leading bit of the field with AIS big-endian encoding. Settling this awaits live testing.

The trailing eight fields may be repeated up to 3 times (for a total of 1 to 4 field groups) to represent up to 4 targets.

IMO289 Marine Traffic Signal

This message provides information on a signal station and status of the control signal at the entrance of a harbor or channel where the shipping direction controlled so that the traffic flow be kept in order.

A message 8 subtype described in [IMO289]. DAC = 001 FID = 19. Fixed length: 360 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 19

56-65

10

Message Linkage ID

linkage

u

Unsigned integer

66-185

120

Name of Signal Station

station

t

20 6-bit chars

186-210

25

Longitude

lon

I3

Unit = minutes * 0.001 181000 = N/A (default) E positive, W negative.

211-234

24

Latitude

lat

I3

Unit = minutes * 0.001 91000 = N/A (default) N positive, S negative.

235-236

2

Status of Signal

status

u

0=N/A (default 1 = In regular service 2 = Irregular service 3 = Reserved for future use

237-241

5

Signal In Service

signal

e

See "Marine Traffic Signals"

242-246

5

UTC hour

hour

u

0-23, 24=N/A (default)

247-252

6

UTC minute

minute

u

0-59, 60=N/A (default)

253-257

5

Expected Next Signal

nextsignal

e

See "Marine Traffic Signals"

258-359

102

Spare

x

Not used
Table 30. Marine Traffic Signals
Code Position Fix Type

0

N/A (default)

1

IALA port traffic signal 1: Serious emergency – all vessels to stop or divert according to instructions.

2

IALA port traffic signal 2: Vessels shall not proceed.

3

IALA port traffic signal 3: Vessels may proceed. One way traffic.

4

IALA port traffic signal 4: Vessels may proceed. Two way traffic.

5

IALA port traffic signal 5: A vessel may proceed only when it has received specific orders to do so.

6

IALA port traffic signal 2a: Vessels shall not proceed, except that vessels which navigate outside the main channel need not comply with the main message.

7

IALA port traffic signal 5a: A vessel may proceed only when it has received specific orders to do so; except that vessels which navigate outside the main channel need not comply with the main message.

8

Japan Traffic Signal - I = "in-bound" only acceptable.

9

Japan Traffic Signal - O = "out-bound" only acceptable.

10

Japan Traffic Signal - F = both "in- and out-bound" acceptable.

11

Japan Traffic Signal - XI = Code will shift to "I" in due time.

12

Japan Traffic Signal - XO = Code will shift to "O" in due time.

13

Japan Traffic Signal - X = Vessels shall not proceed, except a vessel which receives the direction from the competent authority.

14-31

Reserved

IMO289 Weather observation report from ship

There are two variants of this message. They are distinguished by bit 56, the WMO bit. Field layouts after that bit vary depending on it.

A message 8 subtype described in [IMO289]. DAC = 001 FID = 21. Fixed length: 360 bits.

Table 31. Weather observation report from ship: Non-WMO variant
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 21

56-56

1

Variant

wmo

b

Constant: 0 in this variant

57-176

120

Location

location

t

20 6-bit characters

177-201

25

Longitude

lon

I3

Unit = minutes * 0.001, 181000 = N/A (default), E positive, W negative.

202-225

24

Latitude

lat

I3

Unit = minutes * 0.001, 91000 = N/A (default), N positive, S negative.

226-230

5

UTC Day

day

u

1-31, 0=N/A (default)

231-235

5

UTC hour

hour

u

0-23, 24=N/A (default)

236-241

6

UTC minute

minute

u

0-59, 60=N/A (default)

242-245

4

Present Weather

weather

u

wmocode: 0-15

246-246

1

Visibility Limit

vislimit

b

See below

247-253

7

Horiz. Visibility

visibility

U1

0.0-12.6nm, units = nm*0.1, 127 = N/A (default).

254-260

7

Relative Humidity

humidity

u

0-100%: units of 1%, 127 = N/A (default).

261-267

7

Average Wind Speed

wspeed

u

10-min avg wind speed knots, 127 = N/A (default).

268-276

9

Wind Direction

wdir

u

0-359, deg. fom true north, 360 = N/A (default).

277-285

9

Air Pressure

pressure

u

800-1200hPa: units 1hPa, 402 = pressure >= 1201 hPa, 403 - N/A (default), else add 400 to value,

286-289

4

Pressure Tendency

pressuretend

u

WMO FM13 code

290-300

11

Air Temperature

airtemp

I1

Dry bulb temp: units 0.1C, -60.0 to +60.0, -1024 = N/A (default).

301-310

10

Water Temperature

watertemp

I1

-10.0 to 50.0 in 0.1 C, 601 = N/A (default), else -10C after scaling.

311-316

6

Wave period

waveperiod

u

Seconds: 0-60, 63 = N/A (default).

317-324

8

Wave height

waveheight

U1

0-25m in units of 0.1m, 255 = N/A (default).

325-333

9

Wave direction

wavedir

u

0-359: deg. from true north, 360 = N/A (default).

334-341

8

Swell height

swellheight

U1

0-25m: units 0.1m, 255 = N/A (default)

342-350

9

Swell direction

swelldir

u

0-359: deg, fom true north, 360 = N/A (default).

351-356

6

Swell period

swellperiod

u

Seconds: 0-60, 63 = N/A (default).

357-359

3

Spare

x

Not used

The vislimit bit, when on, indicates that the maximum range of the visibility equipment was reached and the visibility reading shall be regarded as > x.x NM.

The standard ([IMO289]) does not list the WMO FM13 codes. The following table applies:

Table 32. Weather observation report from ship: WMO Code 45501
Code Precipitation Type

0

Clear (no clouds at any level)

1

Cloudy

2

Rain

3

Fog

4

Snow

5

Typhoon/hurricane

6

Monsoon

7

Thunderstorm

8

N/A (default)

9-15

Reserved for future use
Table 33. Weather observation report from ship: WMO variant
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 21

56-56

1

Variant

wmo

u

Constant: 1 in this variant

57-72

16

Longitude

lon

I3

Unsigned: minutes * 0.01, E positive, W negative, Lon = (value / 100) – 180, 65536 = N/A (default).

73-87

15

Latitude

lat

I3

Unsigned: minutes * 0.01, N positive, S negative, Lat = (value / 100) – 90, 32767 = N/A (default).

88-91

4

UTC Month

month

u

1-12, 15=N/A (default)

92-97

6

UTC Day

day

u

1-31, 63=N/A (default)

98-102

5

UTC hour

hour

u

0-23, 31=N/A (default)

103-105

3

UTC minute

minute

u

0-50, 7=N/A (default), Minute = (value * 10).

106-112

7

Course Over Ground

course

u

0-359, unit = 1 degree, average over last 10 minutes.

113-117

5

Speed Over Ground

speed

U1

0-14.5m/s: SOG = (value * 0.5) for 0-29, 30 = 15 m/s and more, average over last 10 minutes. 31 = N/A (default)

118-124

7

Heading of the ship

heading

u

5-360: units of 5 degrees, HDT = (value * 5) for 1-72, average over last 10 minutes. 127 = N/A (default)

125-135

11

Pressure at sea level

pressure

U1

90-1100 hPa: P = (value/10)+900 for 0-2000

136-145

10

Pressure Change

pdelta

U1

-50-+50hPa: units of 0.1hPa, d = (value/10)-50 for 0-100, averaged over last 3 hours. 1023 = N/A (default)

146-149

4

Pressure Tendency

ptend

u

WMO BUFR table 010063: Averaged over last 3 hours, 0-8, 15 = N/A.

150-156

7

True Wind Direction

twinddir

u

005-360: deg: average over last 10 minutes, dir = (value*5), value 1-72, 0 = calm, 127 = N/A (default).

157-164

8

True Wind Speed

twindspeed

u

0-127 m/s: average over last 10 mins, speed = value * 0.5, 255 = N/A (default).

165-171

7

Relative Wind Direction

rwinddir

u

005-360 deg: average over last 10 mins, dir = (value*5) for 1-72, 0 = calm, 127 = N/A (default).

172-179

8

Relative Wind Speed

rwindspeed

U1

0-127 m/s: average over last 10 mins, speed = val*0.5 for 0-254, 255 = N/A (default).

180-187

8

Maximum Gust Speed

mgustspeed

U1

0-127 m/s: speed = val*0.5 for 0-254, 255 = N/A (default),

188-194

7

Maximum Gust Direction

mgustdir

u

05-360 deg: dir = (value*5) for 1-72, 0 = calm, 127 = N/A (default).

195-204

10

Air Temperature

airtemp

U1

Dry bulb temp: units 0.1C, 223-323K (c.-50C - +50C). T = (val/10)+223 for 0-1000, 1023 = N/A (default).

205-211

7

Relative Humidity

humidity

u

0-100%: units of 1%, 127 = N/A (default).

212-220

9

Sea Surface Temperature

surftemp

U1

268-318K (c.-5C - +45C): T = (val/10)+268 for 0-500, 511 = N/A (default).

221-226

6

Horiz. Visibility

visibility

U2

0-50000m, Vis = (val**2)*13.073 for 0-62, 63 = N/A (default).

227-235

9

Present Weather

weather

u

BUFR table 020003: Codes 0-510, 511 = N/A (default).

236-240

5

Past Weather 1

pweather1

u

BUFR table 020005: Codes 0-30, 31 = N/A (default).

241-245

5

Past Weather 2

pweather2

u

BUFR table 020004: Codes 0-30, 31 = N/A (default).

246-249

4

Total Cloud Cover

totalcloud

u

0-100%: Cover = val * 10% for 0-10, 15 = N/A (default.)

250-253

4

Cloud amount (low)

lowclouda

u

0-14: BUFR table 020011: 15 = N/A (default).

254-259

6

Cloud type (low)

lowcloudt

u

0-62: BUFR table 020012: 63 = N/A (default).

260-265

6

Cloud type (middle)

midcloudt

u

0-62: BUFR table 020012: 63 = N/A (default).

266-271

6

Cloud type (high)

highcloudt

u

0-62: BUFR table 020012: 63 = N/A (default).

272-278

7

Height of cloud base

cloudbase

U2

0-2500m: h = (value*2).0.16 for 0-125, 126 = more than 2500m, 127 = N/A (default).

279-283

5

Period of Wind Waves

wwperiod

u

0-30s: 31 = N/A (default).

284-289

6

Height of Wind Waves

wwheight

u

Height in meters: 0-30, h = (value * 0.5) for 0-60, 63 = N/A (default).

290-295

6

First Swell Direction

swelldir1

u

10-360 deg: dir = (value*10) for 1-36, 0 = calm, 63 = N/A (default).

296-300

5

First Swell Period

swperiod1

u

Period in seconds: 0-30, 31 = N/A (default).

301-306

6

First Swell Height

swheight1

U1

Height in meters: 0-30, h = (value * 0.5) for 0-60, 63 = N/A (default).

307-312

6

Second Swell Direction

swelldir2

u

10-360 deg: dir = (value*10) for 1-36, 0 = calm, 63 = N/A (default).

313-317

5

Second Swell Period

swperiod2

u

Period in seconds: 0-30, 31 = N/A (default).

318-323

6

Second Swell Height

swheight2

U1

Height in meters: 0-30, h = (value * 0.5) for 0-60, 63 = N/A (default).

324-330

7

Ice deposit (thickness)

icedeposit

u

Thickness: 0-126cm, 127 = N/A (default).

331-333

3

Rate of Ice Accretion

icerate

u

0-6: BUFR table 020032: 7 = N/A (default).

334-336

3

Cause of Ice Accretion

icecause

u

0-6: BUFR table 020033: 7 = N/A (default).

337-341

5

Sea Ice Concentration

seaice

u

0-30: BUFR table 020034: 31 = N/A (default).

342-345

4

Amount and Type of Ice

icetype

u

0-14: BUFR table 020035: 15 = N/A (default).

346-350

5

Ice Situation

icestate

u

0-30: BUFR table 020036: 31 = N/A (default).

351-355

5

Ice Development

icedevel

u

0-30: BUFR table 020037: 31 = N/A (default).

356-359

4

Bearing of Ice Edge

icebearing

u

Bearing: 45-360 deg, dir = (value*45) for 1-8, 15 = N/A (default).

The "minute" entry actually only identifies the end of a 10-minute interval.

In [IMO289], the Latitude formula is given as "Lat = (value / 100) – 9000". This is incorrect; the decrement needs to be 90 for the range to be -90..+90.

Swell directions are arrival directions.

IMO289 Area Notice (broadcast)

This should be used to broadcast time- and location-dependent information about hazards to navigation. For information-lifetime restrictions and usage guidance, refer to [ITU1371].

A message 8 subtype. DAC = 001 FID = 22. 196 to 981 bits. There is a related Message 6 subtype for addressed use.

The message consists of a fixed-length header of 111 bits, followed by 1 to 10 sub-area indications which are fixed-length records 87 bits long. Here is the message header format:

Table 34. Area Notice (addressed) message header
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 22

56-65

10

Message Linkage ID

linkage

u

Unsigned integer

66-72

7

Notice Description

notice

u

See table below

73-76

4

Month (UTC)

month

u

1-12; 0 = N/A (default)

77-81

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

82-86

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

87-92

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

93-110

18

Duration

duration

u

In minutes, 262143 = N/A (default), 0 = cancel this notice.

111-113

3

Subarea shape #1

subarea type

u

0-5 (see "Subarea Types")

114-197

84

Subarea payload #1

shape data

array

See "Subarea Payloads"

198-200

3

Subarea shape #2

subarea type

u

0-5 (see "Subarea Types")

201-284

84

Subarea payload #2

shape data

array

See "Subarea Payloads"

285-287

3

Subarea shape #3

subarea type

u

0-5 (see "Subarea Types")

288-371

84

Subarea payload #3

shape data

array

See "Subarea Payloads"

372-374

3

Subarea shape #4

subarea type

u

0-5 (see "Subarea Types")

375-458

84

Subarea payload #4

shape data

array

See "Subarea Payloads"

459-461

3

Subarea shape #5

subarea type

u

0-5 (see "Subarea Types")

462-545

84

Subarea payload #5

shape data

array

See "Subarea Payloads"

546-548

3

Subarea shape #6

subarea type

u

0-5 (see "Subarea Types")

549-632

84

Subarea payload #6

shape data

array

See "Subarea Payloads"

633-635

3

Subarea shape #7

subarea type

u

0-5 (see "Subarea Types")

636-719

84

Subarea payload #7

shape data

array

See "Subarea Payloads"

720-722

3

Subarea shape #8

subarea type

u

0-5 (see "Subarea Types")

723-806

84

Subarea payload #8

shape data

array

See "Subarea Payloads"

807-809

3

Subarea shape #9

subarea type

u

0-5 (see "Subarea Types")

810-893

84

Subarea payload #9

shape data

array

See "Subarea Payloads"

894-896

3

Subarea shape #10

subarea type

u

0-5 (see "Subarea Types")

897-980

84

Subarea payload #10

shape data

array

See "Subarea Payloads"

The sub-area indications are as described under the addressed form, message type 6 with DAC = 1 and FID = 23.

IMO289 Extended Ship Static and Voyage Related Data

This message should be used by a ship to report the height over keel.

A message 8 subtype. DAC = 001 FID = 24 in [IMO289]. Fixed length, 360 bits. Replaces a deprecated trial message from [IMO236].

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

Source MMSI

mmsi

u

9 digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 24

56-65

10

Message Linkage ID

linkage

u

Unsigned integer

66-78

13

Air Draught

airdraught

u

Unsigned int, in 0.01m 1-81.9 m. 0 = N/A (default) 81.91 = >= 81.91 m

79-108

30

Last Port Of Call

lastport

t

5 6-bit chars, UN locode

109-138

30

Next Port Of Call

nextport

t

5 6-bit chars, UN locode

139-168

30

Second Port Of Call

secondport

t

5 6-bit chars, UN locode

169-170

2

AIS Class A

ais_state

e

See "SOLAS Status"

171-172

2

Automatic Tracking Aid

ata_state

e

See "SOLAS Status"

173-174

2

BNWAS

bnwas_state

e

See "SOLAS Status"

175-176

2

ECDIS Back-up

ecdisb_state

e

See "SOLAS Status"

177-178

2

Paper Nautical Chart

chart_state

e

See "SOLAS Status"

179-180

2

Echo sounder

sounder_state

e

See "SOLAS Status"

181-182

2

Electronic plotting aid

epaid_state

e

See "SOLAS Status"

183-184

2

Emergency steering gear

steer_state

e

See "SOLAS Status"

185-186

2

GNSS

gnss_state

e

See "SOLAS Status"

187-188

2

Gyro compass

gyro_state

e

See "SOLAS Status"

189-190

2

LRIT

lrit_state

e

See "SOLAS Status"

191-192

2

Magnetic compass

magcomp_state

e

See "SOLAS Status"

193-194

2

NAVTEX

navtex_state

e

See "SOLAS Status"

195-196

2

Radar (ARPA)

arpa_state

e

See "SOLAS Status"

197-198

2

Radar (S-band)

sband_state

e

See "SOLAS Status"

199-200

2

Radar (X-band)

xband_state

e

See "SOLAS Status"

201-202

2

Radio HF

hfradio_state

e

See "SOLAS Status"

203-204

2

Radio INMARSAT

inmarsat_state

e

See "SOLAS Status"

205-206

2

Radio MF

mfradio_state

e

See "SOLAS Status"

207-208

2

Radio VHF

vhfradio_state

e

See "SOLAS Status"

209-210

2

Speed Log over ground

grndlog_state

e

See "SOLAS Status"

211-212

2

Speed Log through water

waterlog_state

e

See "SOLAS Status"

213-214

2

THD

thd_state

e

See "SOLAS Status"

215-216

2

Track control system

tcs_state

e

See "SOLAS Status"

217-218

2

VDR/S-VDR

vdr_state

e

See "SOLAS Status"

219-220

2

Reserved

x

Not used

221-224

4

Ice Class

iceclass

e

See "Ice Class"

225-242

18

Shaft Horsepower

horsepower

u

Total ship HP: 1hp units, 262,142 = >= 262,142hp, 262,143 = N/A (default).

243-254

12

VHF Working Channel

vhfchan

u

Channel number, 0 = N/A (default).

255-296

42

Lloyd’s Ship Type

lshiptype

t

7 six-bit characters

297-314

18

Gross Tonnage

tonnage

u

0-262,141, 262,142 = >= 262,142hp, 262,143 = N/A (default).

315-316

2

Laden or Ballast

lading

e

0 = N/A (default), 1 = Laden, 2 = Ballast, 3 = Not in use.

317-318

2

Heavy Fuel Oil Bunkered

heavyoil

e

0 = N/A (default), 1 = No, 2 = Yes, 3 = Not in use.

319-320

2

Light Fuel Oil Bunkered

lightoil

e

0 = N/A (default), 1 = No, 2 = Yes, 3 = Not in use.

321-322

2

Diesel Oil Bunkered

dieseloil

e

0 = N/A (default), 1 = No, 2 = Yes, 3 = Not in use.

323-336

14

Total Bunker Oil

totaloil

u

0-16381 in tonnes, 16382 = >= 16382 tonnes, 16382 = N/A (default).

337-349

13

Number of persons

persons

u

0 = N/A (default), 1-8190, 8191 = >= 8191.

350-359

10

Spare

x

Not used

IMO289 says air draught is in 0.1m steps, but this is incompatible with the two digits of precision in the range.

The special value of 81.91 for air draught in [IMO289], also implies the step size is really 0.01m.

The 2-bit _state fields describe the operational state of various sorts of SOLAS-required navigational equipment. GNSS systems may include GPS, Loran-C, or GLONASS. BNWAS is the Bridge Navigational Watch Alarm System. THD is a Transmitting Heading Device. Paper Nautical Chart state is officially "ECDIS/Paper Nautical Chart" state in [IMO289]. Status codes should be interpreted according to the following table:

Table 35. SOLAS Status
Code Meaning

0

Not available or requested (default)

1

Equipment operational

2

Equipment not operational

3

No data (equipment may or may not be on board/or its status is unknown)
Table 36. Ice Class
Code Meaning

0

Not classified

1

IACS PC 1

2

IACS PC 2

3

IACS PC 3

4

IACS PC 4

5

IACS PC 5

6

IACS PC 6 / FSICR IA Super / RS Arc5

7

IACS PC 7 / FSICR IA / RS Arc4

8

FSICR IB / RS Ice3

9

FSICR IC / RS Ice2

10

RS Ice1

11-14

Reserved for future use

15

Not available = default

ACS = International Association of Classification Societies

PC = Polar Class. For further details, see IACS Req. 2007 Requirements concerning POLAR CLASS and MSC/Circ.1056 and MEPC/Circ.399 on Guidelines for ships operating in Arctic ice-covered waters.

FSICR = Finnish-Swedish Ice Class Rules. For further details, see Finnish Maritime Administration’s Bulletin No.10/10.12.2008 Ice class regulations 2008 (Finnish-Swedish ice class rules). Note: Authorized classification society equivalents for the Finnish-Swedish Ice Class Rules should also be recognized, as issued in the Finnish Maritime Administration’s Bulletin No.4/2.4.2007 (as amended). Both bulletins can be found at www.fma.fi.

RS = Russian Maritime Register of Shipping. For further details see Rules for the classification and construction of seagoing ships, Edition 2008.

VHF channel number is encoded according to Recommendation ITU-R M.1084.

The lshiptype field uses Lloyd’s Register STATCODE 5 encoding.

IMO289 Environmental

A message 8 subtype. DAC = 001 FID = 26. Variable length: 168-1008 bits.

Table 37. Environmental message header
Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 26

56

reports

a5

Sensor records array

0-3

4

Sensor Report Type

sensor

u

See table below

4-8

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

9-13

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

14-19

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

20-26

7

Site ID

site

u

Binary ID of sensor site

27-111

85

Sensor payload

payload

d

Sensor payload data

The fixed header is followed by 1-5 sensor records, each 112 bits long. The Sensor Report Type is interpreted as follows, and controls the interpretation of the sensor payload data.

Table 38. Sensor report types

0

Site location

1

Station ID

2

Wind

3

Water level

4

Current flow (2D)

5

Current flow (3D)

6

Horizontal current flow

7

Sea state

8

Salinity

9

Weather

10

Air gap/Air draft

11

(reserved for future use)

Here are the payload types for each variant:

Table 39. Site location payload
Field Len Description Member T Units

0-27

28

Longitude

lon

I4

As in Common Navigation Block

28-54

27

Latitude

lat

I4

As in Common Navigation Block

55-65

11

Altitude

alt

u

Sensor altitude above MSL, 0-200 in units of 0.1m, 2001 = 200.1 m or higher, 2002 = N/A (default), 2003-2046 reserved.

66-69

4

Sensor owner

owner

e

See "Sensor Owner Codes"

70-72

3

Data timeout

timeout

e

See "Data Timeout Codes"

73-84

12

Spare

x

Not used
Table 40. Sensor Owner Codes

0

Unknown (default)

1

Hydrographic office

2

Inland waterway authority

3

Coastal directorate

4

Meteorological service

5

Port Authority

6

Coast guard

7-13

(reserved for future use)

14

(reserved for regional use)
Table 41. Data Timeout Codes

0

No time period (default)

1

10 minutes

2

1 hour

3

6 hours

4

12 hours

5

24 hours

6-7

(reserved for future use)
Table 42. Station ID payload
Field Len Description Member T Units

0

84

Name

name

t

14 chars of six-bit ASCII.

84

1

Spare

x

Not used
Table 43. Wind report payload
Field Len Description Member T Units

0-6

7

Average Wind Speed

wspeed

u

10-min avg wind speed, 0-120 in 1-knot units, 121 = 121 knots or greater, 122 = N/A (default), 123-126 = reserved.

7-13

7

Wind Gust

wgust

u

10-min max wind speed, 0-120 in 1-knot units, 121 = 121 knots or greater, 122 = N/A (default), 123-126 = reserved.

14-22

9

Wind Direction

wdir

u

0-359, degrees fom true north >=360 = N/A (default)

23-31

9

Wind Gust Direction

wgustdir

u

0-359, degrees fom true north >=360 = N/A (default)

32-34

3

Sensor Description

sensortype

e

See "Sensor Types"

35-41

7

Forecast Wind Speed

fwspeed

u

Predicted average wind speed, 0-120 in 1-knot units, 121 = 121 knots or greater, 122 = N/A (default), 123-126 = reserved.

42-48

7

Forecast Wind Gust

fwgust

u

Predicted max wind speed, 0-120 in 1-knot units, 121 = 121 knots or greater, 122 = N/A (default), 123-126 = reserved.

49-57

9

Forecast Wind Direction

fwdir

u

0-359, degrees fom true north >=360 = N/A (default)

58-62

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

63-67

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

68-73

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

74-81

8

Duration

duration

u

Forecast duration in minutes, 255 = N/A (default), 0 = cancel forecast.

82-84

3

Spare

x

Not used

The timestamp group is intended as a valid time of forecast.

Table 44. Sensor Types

0

No data (default)

1

Raw real time

2

Real time with quality control

3

Predicted (based on historical statistics)

4

Forecast (predicted, refined with real-time information)

5

Nowcast (a continuous forecast)

6

(reserved for future use)

7

Sensor not available
Table 45. Water level report payload
Field Len Description Member T Units

0-0

1

Water Level Type

absolute

b

False if relative to reference datum.

1-16

16

Water Level

level

i

In 0.01 meter steps, -327.67 to 327.67, -32767 = -327.67m or less, 32767 = 327.67m or more, -32768 = N/A (default).

17-18

2

Water Level Trend

leveltrend

u

0 = increasing, 1 = decreasing, 2 = steady, 3 = N/A (default).

19-23

5

Vertical Reference Datum

datum

u

See table below

24-26

3

Sensor Description

sensortype

e

See "Sensor Types"

27-27

1

Forecast Water Level Type

absolute

b

False if relative to reference datum.

28-43

16

Forecast Water Level

level

i

In 0.001 meter steps, -327.67 to 327.67, -32767 = -327.67m or less, 32767 = 327.67m or more, -32768 = N/A (default).

44-48

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

49-53

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

54-59

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

60-67

8

Duration

duration

u

Forecast duration in minutes, 255 = N/A (default), 0 = cancel forecast.

68-84

17

Spare

x

Not used

IMO289 says water level is in 0.1m steps, but this is incompatible with the two digits of precision in the range.

The timestamp group is intended as a valid time of forecast.

Table 46. Vertical Reference Datum

0

Mean Lower Low Water (MLLW)

1

International Great Lakes Datum (IGLD-85)

2

Local river datum

3

Station Datum (STND)

4

Mean Higher High Water (MHHW)

5

Mean High Water (MHW)

6

Mean Sea Level (MSL)

7

Mean Low Water (MLW)

8

National Geodetic Vertical Datum (NGVD-29)

9

North American Vertical Datum (NAVD-88)

10

World Geodetic System (WGS-84)

11

Lowest Astronomical Tide (LAT)

12

pool

13

gauge

14

Unknown/not available (default)

15-30

Reserved for future use
Table 47. Current flow (2D) report payload
Field Len Description Member T Units

0-7

8

Current Speed #1

cspeed1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

8-16

9

Current Direction #1

cdir1

u

0-359: deg from true north, >=360 = N/A (default).

17-25

9

Measurement Depth #1

cdepth1

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

26-33

8

Current Speed #2

cspeed2

U1

0.0-24.5 knots, units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

34-42

9

Current Direction #2

cdir2

u

0-359: deg. fom true north, >=360 = N/A (default)

43-51

9

Measurement Depth #2

cdepth2

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

52-59

8

Current Speed #3

cspeed3

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

60-68

9

Current Direction #3

cdir3

u

0-359: degrees fom true north, >=360 = N/A (default).

69-77

9

Measurement Depth #3

cdepth3

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

78-80

3

Sensor Description

sensortype

e

See "Sensor Types"

81-84

4

Spare

x

Not used
Table 48. Current flow (3D) payload
Field Len Description Member T Units

0-7

8

Current Vector component North (u) #1

cnorth1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

8-15

8

Current Vector component East (v) #1

ceast1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

16-23

8

Current Vector component Up (z) #1

cup1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

24-32

9

Measurement Depth #1

cdepth1

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

33-40

8

Current Vector component North (u) #2

cnorth2

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

41-48

8

Current Vector component East (v) #2

ceast2

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

49-56

8

Current Vector component Up (z) #2

cup2

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

57-65

9

Measurement Depth #2

cdepth2

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

66-68

3

Sensor Description

sensortype

e

See "Sensor Types"

69-84

16

Spare

x

Not used
Table 49. Horizontal current report payload
Field Len Description Member T Units

0-8

9

Current Bearing #1

bearing1

u

0-359: deg from true north, >=360 = N/A (default).

9-15

7

Current Distance #1

distance1

u

0-120m: 121 = 121m or greater, 122 = N/A (default), 123-127 (reserved).

16-23

8

Current Speed #1

speed1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

24-32

9

Current Direction #1

direction1

u

0-359: deg from true north, >=360 = N/A (default).

33-41

9

Measurement Depth #1

depth1

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

42-50

9

Current Bearing #2

bearing1

u

0-359: deg from true north, >=360 = N/A (default).

51-57

7

Current Distance #2

distance1

u

0-120m: 121 = 121m or greater, 122 = N/A (default), 123-127 (reserved).

58-65

8

Current Speed #2

speed1

U1

0.0-24.5 knots: units 0.1 knots, 246 = speed >= 24.6 knots, 247 = N/A (default), 248-255 (reserved).

66-74

9

Current Direction #2

direction1

u

0-359: deg from true north, >=360 = N/A (default).

75-83

9

Measurement Depth #2

depth1

u

0-360m down: units 1m, 361 = 361m or greater, 362 = N/A (default), 363-511 (reserved).

84-84

1

Spare

x

Not used
Table 50. Sea state report payload
Field Len Description Member T Units

0-7

8

Swell Height

swheight

U1

Units 0.1m: 0.0-24.5m, 246 = height >= 24,6m, 247 = N/A (default), 248-255 reserved, else h = (value * 0.5).

8-13

6

Swell Period

swperiod

u

Period in seconds: 0-60, 61 = N/A (default), 62-63 (reserved).

14-22

9

Swell Direction

swelldir

u

0-359 deg: 0-359 true bearing, 360 = N/A (default), 361-511 reserved,

23-26

4

Sea State

seastate

u

Beaufort scale: 0-12 >= 13 = N/A (default)

27-29

3

Swell Sensor Description

swelltype

e

See "Sensor Types"

30-39

10

Water Temperature

watertemp

U1

-10.0 to 50.0: units 0.1 C, >=601 = N/A (default). 602-1023 reserved, else -10.0m after scaling.

40-46

7

Water Temperature Depth

distance1

U1

0.0-12.0m: 0.1m units, 121 = 12.1m or greater, 122 = N/A (default), 123-126 (reserved).

47-49

3

Depth Sensor Description

depthtype

e

See "Sensor Types"

50-57

8

Wave Height

waveheight

U1

Height 0.0-24.5m: units 0.1m, 246 = height >= 24.6m, 247 N/A (default), 248-255 reserved.

58-63

6

Wave Period

waveperiod

u

0-60: units of seconds, 61 = N/A (default), 62-63 reserved.

64-72

9

Wave Direction

wavedir

u

0-359: true bearing, 360 = N/A (default), 361-511 reserved.

73-75

3

Wave Sensor Description

wavetype

e

See "Sensor Types"

76-84

9

Salinity

salinity

U1

0.0-50.0%: units of 0.1% 501 = salinity >= 50.1% 502 = data N/A (default) 503 - sensor N/A, 504-511 reserved.

The standard does not fix the meaning of a water temperature depth of 127.

Table 51. Salinity report payload
Field Len Description Member T Units

0-9

10

Water Temperature

watertemp

U1

-10.0 to 50.0: units 0.1 C, >=601 = N/A (default). 602-1023 reserved, else -10.0m after scaling.

10-19

10

Conductivity

conductivity

U1

In Siemens/m, 0.0-7.0, 0.1 S/m steps, 701 = not less than 7.01, 702 = data N/A, 703 = sensor N/A (default), 704-1023 (reserved).

20-35

16

Water Pressure

pressure

U1

Water pressure: 0.0-6000.0, 0.1 decibar steps, 60001 = pressure >= 6000.1, 60002 = data N/A, 60003 = sensor N/A (default), 60004-65536 reserved.

36-44

9

Salinity

salinity

U1

0.0-50.0%: units of 0.1% 501 = salinity >= 50.1% 502 = data N/A (default) 503 - sensor N/A, 504-511 reserved.

45-46

2

Salinity Type

salinitytype

e

0 = measured, 1 = calculated using PSS-78, 2 = calculated using other method, 3 = reserved.

47-49

3

Sensor Description

sensortype

e

See "Sensor Types"

50-84

35

Spare

x

Not used

No default is specified for salinity type.

Table 52. Weather report payload
Field Len Description Member T Units

0-10

11

Air Temperature

temperature

i

Dry bulb temp: 0.1 deg C -60.0 to +60.0, -1024 = data N/A (default), 601-1023 reserved.

11-13

3

Temp. Sensor Type

sensortype

e

See "Sensor Types"

14-15

2

Precipitation Type

preciptype

e

0 = rain, 1 = rain and snow, 2 = rain and snow, 3 = other.

16-23

8

Horiz. Visibility

visibility

U1

Units of 0.1 nautical miles, 0.0-24.0, 241 = visibility >= 24.1nm, 242 = data N/A, 243 = sensor N/A (default), 244-255 reserved.

24-33

10

Dew Point

dewpoint

i

-20.0 to +50.0: 0.1 deg C, 501 = N/A (default), 502-511 reserved, -511—​201 reserved.

34-36

3

Dewpoint Sensor Type

dewtype

e

See "Sensor Types".

37-45

9

Air Pressure

pressure

u

0 = pressure ⇐ 800hpA, 1-401 = 800-1200hPa, 402 = pressure >= 1201 hPa, 403 - data N/A (default), 404-511 reserved.

46-47

2

Pressure Tendency

pressuretend

e

0 = steady, 1 = decreasing, 2 = increasing, 3 - N/A (default).

48-50

3

Pressure Sensor Type

pressuretype

e

See "Sensor Types"

51-59

9

Salinity

salinity

U1

0.0-50.0%: units of 0.1% 501 = salinity >= 50.1% 502 = data N/A (default) 503 - sensor N/A, 504-511 reserved.

60-84

25

Spare

x

Not used

The standard does not specify how to code 'Precipitation Type' when there is none.

Table 53. Air Gap/Air Draft report payload
Field Len Description Member T Units

0-12

13

Air Draught

airdraught

U1

1-81.9m in 0.01m steps, 8191 = distance >= 81.91m, 0 = N/A (default).

13-25

13

Air Gap

airgap

U1

1-81.9m in 0.01m steps, 8191 = distance >= 81.91m, 0 = N/A (default).

26-27

2

Air Gap Trend

gaptrend

e

0 = steady, 1 = rising, 2 = falling, 3 = N/A (default).

28-40

13

Forecast Air Gap

fairgap

U1

1-81.9m in 0.01m steps, 8191 = distance >= 81.91m, 0 = N/A (default).

41-45

5

Day (UTC)

day

u

1-31; 0 = N/A (default)

46-50

5

Hour (UTC)

hour

u

0-23; 24 = N/A (default)

51-56

6

Minute (UTC)

minute

u

0-59; 60 = N/A (default)

57-84

28

Spare

x

Not used

Air draught is the vertical distance measured from the ship’s waterline to the highest point on the ship. Air gap is the vertical distance measured from the surface of the water to the sensor.

IMO289 says steps are in 0.1m steps, but this is incompatible with the two digits of precision in the range.

The timestamp is for the forecast air gap.

IMO289 Route Information (broadcast)

The content of this message is a time and a list of waypoints describing a course. It has an addressed equivalent that is a message 6 subtype.

A message 8 subtype. DAC = 001 FID = 27. Variable length: 172-997 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 27

56-65

10

Message Linkage ID

linkage

u

Unsigned integer

66-68

3

Sender Class

sender

u

0 = ship (default), 1 = authority, 27 = reserved for future use.

69-73

5

Route Type

rtype

e

See below

74-77

4

Start month

month

u

1-12, 0=N/A (default)

78-82

5

Start day

day

u

1-31, 0=N/A (default)

83-87

5

Start hour

hour

u

0-23, 24=N/A (default)

88-93

6

Start minute

minute

u

0-59, 60=N/A (default)

94-111

18

Duration

duration

u

Minutes from start time, 0 = cancel route, 262,143 = not available (default).

112-116

5

Waypoint count

waycount

u

1-16, values 17-31 are not used.

117

waypoints

a^16

Waypoint array

0-27

28

Longitude

lon

I4

Unit = minutes * 0.0001, 181000 = N/A (default), E positive, W negative.

28-54

27

Latitude

lat

I4

Unit = minutes * 0.001, 91000 = N/A (default), N positive, S negative.

The final pair of fields in the table above is a waypoint. The message may end with 1 to 16 waypoints.

For interpretation of the Route Type field, see the table under the "Route Information (addressed)" message (DAC=1, FID=28).

IMO289 Text description (broadcast)

A message 8 subtype. DAC = 001 FID = 29. Variable length: 72-1032 bits.

Intended to be used to associate a text annotation with another message via the Message Linkage ID field.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 29

56-65

10

Message Linkage ID

linkage

u

Unsigned integer

66-?

6-966

Description

description

t

String

There is an equivalent subtype of message 6 that is an addressed description.

Meteorological and Hydrological Data (IMO289)

A message 8 subtype. DAC = 001 FID = 31. Fixed length, 360 bits. Supersedes an [IMO236] message with the same title but FID = 11 and a different binary layout. The exact differences are: (a) The addition of the Position Accuracy field, (b) water level has 12 bits of precision rather than 9 (units of centimeters rather than decimeters), and (c) end padding changes from 6 to 10 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

DAC

dac

u

DAC = 001

50-55

6

FID

fid

u

FID = 31

56-80

25

Longitude

lon

I3

Unit = minutes * 0.001, E positive, We negative, 181000 = N/A (default).

81-104

24

Latitude

lat

I3

Unit = minutes * 0.001, N positive, S negative, 91000 = N/A (default).

105-105

1

Fix quality

accuracy

b

As in Common Navigation Block

106-110

5

Day

day

u

1-31, 0=N/A (default)

111-115

5

Hour

hour

u

0-23, 24=N/A (default)

116-121

6

Minute

minute

u

0-59, 60=N/A (default)

122-128

7

Average Wind Speed

wspeed

u

10-min avg wind speed: knots, 126 = wind >= 126 knots, 127 = N/A (default).

129-135

7

Gust Speed

wgust

u

10-min max wind speed: knots, 126 = wind >= 126 knots, 127 = N/A (default).

136-144

9

Wind Direction

wdir

u

0-359, true bearing, 360 = N/A (default).

145-153

9

Wind Gust Direction

wgustdir

u

0-359, true bearing, 360 = N/A (default).

154-164

11

Air Temperature

airtemp

I1

Dry bulb temp: units 0.1C, -60.0 to +60.0, -1024 = N/A (default).

165-171

7

Relative Humidity

humidity

u

0-100%: units of 1%, 101 = N/A (default).

172-181

10

Dew Point

dewpoint

I1

-20.0 to +50.0: units 0.1C, 501 = N/A (default).

182-190

9

Air Pressure

pressure

u

800-1200hPa, 1hPa, 0 = pressure ⇐ 799hPa, 402 = pressure >= 1201 hPa, 511 = N/A (default).

191-192

2

Pressure Tendency

pressuretend

e

0 = steady, 1 = decreasing, 2 = increasing, 3 = N/A (default).

193-193

7

Max. visibility

visgreater

b

Visibility greater than.

194-200

8

Horiz. Visibility

visibility

U1

Units are 0.1 nautical miles, 127 = N/A (default).

201-212

12

Water Level

waterlevel

I2

-10.0 to +30.0 in 0.01m, -10.0m after scaling, 4001 = N/A (default).

213-214

2

Water Level Trend

leveltrend

e

0 = steady, 1 = decreasing, 2 = increasing, 3 = N/A (default).

215-222

8

Surface Current Speed

cspeed

U1

0.0-25.0: units 0.1 knot, 251 = speed >= 25.1 knots, 255 = N/A (default).

223-231

9

Surface Current Direction

cdir

u

0-359: deg. from true north, 360 = N/A (default).

232-239

8

Current Speed #2

cspeed2

U1

0.0-25.0 knots: units 0.1 knot, 251 = speed >= 25.1 knots, 255 = N/A (default).

240-248

9

Current Direction #2

cdir2

u

0-359: true bearing, 360 = N/A (default).

249-253

5

Measurement Depth #2

cdepth2

U1

0-30m down: units 0.1m, 31 = N/A (default).

254-261

8

Current Speed #3

cspeed3

U1

0.0-25.0 knots: units 0.1 knot, 251 = speed >= 25.1 knots, 255 = N/A (default).

262-270

9

Current Direction #3

cdir3

u

0-359: true bearing, 360 = N/A (default).

271-275

5

Measurement Depth #3

cdepth3

u

0-30m down: units 0.1m, 31 = N/A (default).

276-283

8

Wave Height

waveheight

U1

Height 0-25m: units 0.1m, 251 = height >= 25.1m, 255 = N/A (default).

284-289

6

Wave Period

waveperiod

u

Seconds, 0-60, units 1s, 63 = N/A (default).

290-298

9

Wave Direction

wavedir

u

0-359: true bearing, 360 = N/A (default).

299-306

8

Swell Height

swellheight

U1

0-25m: units 0.1m, 251 = height >= 25.1m, 255 = N/A (default).

307-312

6

Swell Period

swellperiod

u

0-60, units 1s 360 = N/A (default)

313-321

9

Swell Direction

swelldir

u

0-359: true bearing, 360 = N/A (default)

322-325

4

Sea State

seastate

e

See "Beaufort scale"

326-335

10

Water Temperature

watertemp

I1

-10.0 to 50.0 C: units 0.1 deg, 501 = N/A (default)

336-338

3

Precipitation

preciptype

e

See "Precipitation type"

339-347

9

Salinity

salinity

U1

0.0-50.0%: units of 0.1% 501 = salinity >= 50.1% 510 = N/A (default) 511 = sensor not available

348-349

2

Ice

ice

u

0 = No 1 = Yes 2 = (reserved for future use) 3 = not available = default

350-359

10

Spare

x

Not used

Precipitation types and Beaufort scale are as for the [IMO236] version.

Inland ship static and voyage related data (Inland AIS)

A message 8 subtype. DAC = 200 FID = 10. Fixed length, 168 bits.

This message should be used by inland vessels only to broadcast ship static and voyage related data in addition to message 5. The message should be sent as soon as possible (from the AIS point of view) after message 5.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

Designated Area Code

dac

u

Constant: 200

50-55

6

Functional ID

fid

u

Constant: 10

56-103

48

European Vessel ID

vin

t

8 six-bit characters

104-116

13

Length of ship

length

u

1-8000 * 0.1m, default 0

117-126

10

Beam of ship

beam

u

1-1000 * 0.1m, default 0

127-140

14

Ship/combination type

shiptype

e

ERI Classification

141-143

3

Hazardous cargo

hazard

e

See "Hazard Codes" below

144-154

11

Draught

draught

u

1-200 * 0.01m, default 0

155-156

2

Loaded/Unloaded

loaded

e

See "Load Status" below

157-157

1

Speed inf. quality

speed_q

b

0 = low/GNSS (default) 1 = high

158-158

1

Course inf. quality

course_q

b

0 = low/GNSS (default) 1 = high

159-159

1

Heading inf. quality

heading_q

b

0 = low/GNSS (default) 1 = high

160-167

8

Spare

x

Not used

OPEN-QUESTION: [INLAND] is not explicit whether the "Ship/combination type" field is to contain full ERI codes with range 8000-8370 or ERI SOLAS codes in the range 1-99. The tables below expand both. Full ERI codes have been observed in the wild.

Table 54. ERI Classification
Code SOLAS Description

8000

99

Vessel, type unknown

8010

79

Motor freighter

8020

89

Motor tanker

8021

80

Motor tanker, liquid cargo, type N

8022

80

Motor tanker, liquid cargo, type C

8023

89

Motor tanker, dry cargo as if liquid (e.g. cement)

8030

79

Container vessel

8040

80

Gas tanker

8050

79

Motor freighter, tug

8060

89

Motor tanker, tug

8070

79

Motor freighter with one or more ships alongside

8080

89

Motor freighter with tanker

8090

79

Motor freighter pushing one or more freighters

8100

89

Motor freighter pushing at least one tank-ship

8110

79

Tug, freighter

8120

89

Tug, tanker

8130

31

Tug freighter, coupled

8140

31

Tug, freighter/tanker, coupled

8150

99

Freightbarge

8160

99

Tankbarge

8161

90

Tankbarge, liquid cargo, type N

8162

90

Tankbarge, liquid cargo, type C

8163

99

Tankbarge, dry cargo as if liquid (e.g. cement)

8170

99

Freightbarge with containers

8180

90

Tankbarge, gas

8210

79

Pushtow, one cargo barge

8220

79

Pushtow, two cargo barges

8230

79

Pushtow, three cargo barges

8240

79

Pushtow, four cargo barges

8250

79

Pushtow, five cargo barges

8260

79

Pushtow, six cargo barges

8270

79

Pushtow, seven cargo barges

8280

79

Pushtow, eight cargo barges

8290

79

Pushtow, nine or more barges

8310

80

Pushtow, one tank/gas barge

8320

80

Pushtow, two barges at least one tanker or gas barge

8330

80

Pushtow, three barges at least one tanker or gas barge

8340

80

Pushtow, four barges at least one tanker or gas barge

8350

80

Pushtow, five barges at least one tanker or gas barge

8360

80

Pushtow, six barges at least one tanker or gas barge

8370

80

Pushtow, seven barges at least one tanker or gas barge
Table 55. SOLAS ship type, first digit

3

Vessel

7

Cargo ship

8

Tanker

9

Other types of ship
Table 56. SOLAS ship type, second digit

0

All ships of this type

1

Towing

8

Tanker

9

No additional information
Table 57. Hazard code

0

0 blue cones/lights

1

1 blue cone/light

2

2 blue cones/lights

3

3 blue cones/lights

4

4 B-Flag

5

Unknown (default)
Table 58. Load status

0

N/A (default)

1

Unloaded

2

Loaded

EMMA Warning Report (Inland AIS)

A message 8 subtype. DAC = 200 FID = 23. Fixed length, 256 bits.

The EMMA warning is sent by base stations to drive shipboard ECDIS displays of heavy weather conditions. The following message is capable of transmitting the EMMA data using the AIS channel. It does not replace the Notices to Skippers warnings.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

Designated Area Code

dac

u

Constant: 200

50-55

6

Functional ID

fid

u

Constant: 23

56-63

8

Start Year

start_year

u

1-55, year since 2000 0 = N/A (default)

64-67

4

Start Month

start_month

u

1-12; 0 = N/A (default)

68-72

5

Start Day

start_day

u

1-31; 0 = N/A (default)

73-80

8

End Year

end_year

u

1-55, year since 2000 0 = N/A (default)

81-84

4

End Month

end_month

u

1-12; 0 = N/A (default)

85-89

5

End Day

end_day

u

1-31; 0 = N/A (default)

90-94

5

Start Hour

start_hour

u

0-23; 24 = N/A (default)

95-100

6

Start Minute

start_minute

u

0-59; 60 = N/A (default)

101-105

5

End Hour

end_hour

u

0-23; 24 = N/A (default)

106-111

6

End Minute

end_minute

u

0-59; 60 = N/A (default)

112-139

28

Start Longitude

start_lon

I4

Minutes/10000 (as in CNB)

140-166

27

Start Latitude

start_lat

I4

Minutes/10000 (as in CNB)

167-194

28

End Longitude

end_lon

I4

Minutes/10000 (as in CNB)

195-221

27

End Latitude

end_lat

I4

Minutes/10000 (as in CNB)

222-225

4

Type

type

e

See "EMMA Type Codes" below

226-234

9

Min value

min

i

Signed Integer, see below

235-243

9

Max value

max

i

Signed Integer, see below

244-245

2

Classification

intensity

e

1 = Slight, 2 = Medium, 3 = Strong

246-249

4

Wind Direction

wind

e

See "EMMA Winds" below

250-255

6

Spare

x

Not used

OPEN-QUESTION: [INLAND] is not explicit about the interpretation of the longitude and latitude fields; these semantics are assumed here from 28 and 27-bit fields in other messages.

[INLAND] specifies an 8-bit format with 9th leading sign bit for the min and max fields. Values 0-253 are interpreted as integer data, modified by the leading sign bit. The values +254 and -254 are interpreted as "greater that +253" and "less than -253" respectively. Both values +255 and -255 are interpreted as "unknown" (default).

OPEN-QUESTION: What are the semantics of the min and max values? To what parameters do they apply?

OPEN-QUESTION: [INLAND] does not specify whether start and end times are UTC or local.

Table 59. EMMA Type Codes

0

NA

Not Available

1

WI

Wind

2

RA

Rain

3

SN

Snow and ice

4

TH

Thunderstorm

5

FO

Fog

6

LT

Low temperature

7

HT

High temperature

8

FL

Flood

9

FI

Forest Fire
Table 60. EMMA Winds

1

N

North

2

NE

North East

3

E

East

4

SE

South East

5

S

South

6

SW

South West

7

W

West

8

NW

North West

Water Levels (Inland AIS)

A message 6 subtype. DAC = 200 FID = 24. Fixed length, 168 bits.

This message should be used to inform skippers about actual water levels in their area. It is additional short-term information to the water levels distributed via Notices to Skippers. It is possible to transmit the water levels of more than 4 gauges using multiple messages.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 6

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

Designated Area Code

dac

u

Constant: 200

50-55

6

Functional ID

fid

u

Constant: 24

56-67

12

UN Country Code

country

t

2 six-bit characters

68

gauges

a4

Gauge measurement array

0-10

11

Gauge ID

id

u

0=unknown (default)

11-24

14

Water Level

level

i

cm, 0=unknown (default)

Water levels are relative to the local standard, e.g. GIW in Germany and RNW on the Danube.

Signal Strength (Inland AIS)

A message 8 subtype. DAC = 200 FID = 40. Fixed length, 168 bits.

This message should be sent by base stations only, to inform about the status of different light signals to all vessels in a certain area. The information should be displayed on an external Inland ECDIS display as dynamic symbols. The message should be sent with binary message 8 at regular intervals.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 8

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-49

10

Designated Area Code

dac

u

Constant: 200

50-55

6

Functional ID

fid

u

Constant: 40

56-83

28

Signal Longitude

lon

I4

Minutes/10000 (as in CNB)

84-110

27

Signal Latitude

lat

I4

Minutes/10000 (as in CNB)

111-114

4

Signal form

form

u

Consult [INLAND] Annex C

115-123

9

Signal orientation

facing

u

0-39 deg, 511= N/A (default)

124-126

3

Direction of impact

direction

e

See "Signal Impact" below

127-156

30

Light Status

status

e

See "Signal Status" below

157-167

11

Spare

x

Not used

OPEN-QUESTION: [INLAND] is not explicit about the interpretation of the longitude and latitude fields; these semantics are assumed here from 28 and 27-bit fields in other messages.

The Signal Form field describes the physical arrangement of the signal lights. Values 0 and 15 indicate the shape is unknown or unspecified.

Table 61. Direction of Signal Impact

0

Unknown (default)

1

Upstream

2

Downstream

3

To left bank

4

To right bank

The Signal Status field is interpreted as 9 decimal digits describing the lights as numbered in their Signal Form diagram - typically left to right and then top to bottom - with each digit interpreted in the following way:

Table 62. Signal Status

0

Unknown (default)

1

No light

2

White

3

Yellow

4

Green

5

Red

6

White flashing

7

Yellow flashing.

Type 9: Standard SAR Aircraft Position Report

Tracking information for search-and-rescue aircraft. Total number of bits is 168.

Field Len Description Member T Encoding

0-5

6

Message Type

type

u

Constant: 9

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

MMSI

mmsi

u

9 decimal digits

38-49

12

Altitude

alt

u

See below

50-59

10

SOG

speed

u

See below

60-60

1

Position Accuracy

accuracy

u

See below

61-88

28

Longitude

lon

I4

Minutes/10000 (as in CNB)

89-115

27

Latitude

lat

I4

Minutes/10000 (as in CNB)

116-127

12

Course Over Ground

course

U1

True bearing, 0.1 degree units

128-133

6

Time Stamp

second

u

UTC second.

134-141

8

Regional reserved

regional

x

Reserved

142-142

1

DTE

dte

b

0=Data terminal ready, 1=Data terminal not ready (default)

143-145

3

Spare

x

Not used

146-146

1

Assigned

assigned

b

Assigned-mode flag

147-147

1

RAIM flag

raim

b

As for common navigation block

148-167

20

Radio status

radio

u

See [IALA] for details.

Altitude is in meters. The special value 4095 indicates altitude is not available; 4094 indicates 4094 meters or higher.

Speed over ground is in knots, not deciknots as in the common navigation block; planes go faster. The special value 1023 indicates speed not available, 1022 indicates 1022 knots or higher.

Position Accuracy, Longitude, Latitude, and Course over Ground are encoded identically as in the common navigation block and are even at the same bit offsets. Time stamp has the same special values as in the common navigation block, but is at a different offset.

Type 10: UTC/Date Inquiry

Request for UTC/Date information from an AIS base station. Total number of bits is 72.

Field Len Description Member T Encoding

0-5

6

Message Type

type

u

Constant: 10

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70-71

2

Spare

x

Not used

Type 11: UTC/Date Response

Identical to message 4, with the semantics of a response to inquiry.

Type 12: Addressed Safety-Related Message

This is a point-to-point text message. The payload is interpreted as six-bit text. This message is variable in length up to a maximum of 1008 bits (up to 5 AIVDM sentence payloads).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 12

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Sequence Number

seqno

u

Unsigned integer 0-3

40-69

30

Destination MMSI

dest_mmsi

u

9 decimal digits

70

1

Retransmit flag

retransmit

b

0 = no retransmit (default), 1 = retransmitted

71

1

Spare

x

Not used

72

936

Text

text

t

1-156 chars of six-bit text. May be shorter than 936 bits.

Pragmatic note: On [AISHUB] the actual content of these messages is highly variable, ranging from fairly plain English ("PLEASE REPORT TO JOBOURG TRAFFIC CHANNEL 13") through snippets of tabular data ("PAX 589 FG 36 IX 74 MOTO 10 CREW 108+1" through what look like opaque commercial codes ("EP285 IX46 FG3 DK8 PL56") to empty strings and content that looks like line noise ("]XFD5D/\7`>PA!Q DX0??K?8?>D").

Such apparently garbled content does not mean there is an error in your decoder. It may indicate faulty encoders, operator error, or even the use of private encodings for non-ASCII character sets.

Type 13: Safety-Related Acknowledgment

Message type 13 is a receipt acknowledgement to senders of previous messages of type 12. The message layout is identical to a type 7 Binary Acknowledge.

Type 14: Safety-Related Broadcast Message

This is a broadcast text message. The payload is interpreted as six-bit text. This message is variable in length up to a maximum of 1008 bits (up to 5 AIVDM sentence payloads).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 14

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40

968

Text

text

t

1-161 chars of six-bit text. May be shorter than 968 bits.

Note: 161 * 6 = 966. [IALA] specifies 968 because over-the-air messages are required to be padded to an 8-bit byte boundary by [ITU1371].

Also see the pragmatic note on message content attached to type 12; it applies to type 14 messages as well.

Type 15: Interrogation

Message type 15 is used by a base station to query one or two other AIS transceivers for status messages of specified types. "Source MMSI" is the interrogating station. 88-160 bits depending on the number of queries.

This message is probably not interesting unless you are doing traffic analysis of information flow in an AIS station network. The "slot offset" members are a request for the response to interrogation to occupy a particular time division in the TDMA packet layer.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 15

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-69

30

Interrogated MMSI

mmsi1

u

9 decimal digits

70-75

6

First message type

type1_1

u

Unsigned integer

76-87

12

First slot offset

offset1_1

u

Unsigned integer

88-89

2

Spare

x

Not used

90-95

6

Second message type

type1_2

u

Unsigned integer

96-107

12

Second slot offset

offset1_2

u

Unsigned integer

108-109

2

Spare

x

Not used

110-139

30

Interrogated MMSI

mmsi2

u

9 decimal digits

140-145

6

First message type

type2_1

u

Unsigned integer

146-157

12

First slot offset

offset2_1

u

Unsigned integer

158-159

2

Spare

x

Not used

There are four use cases for this message. A decoder must dispatch on the length of the data packet to determine which it is seeing:

  1. One station is interrogated for one message type. Length is 88 bits.

  2. One station is interrogated for two message types, Length is 110 bits. There is a design error in the standard here; according to the [ITU1371] requirement for padding to 8 bits, this should have been 112 with a 4-bit trailing spare field, and decoders should be prepared to handle that length as well. See the discussion of byte alignment elsewhere in this document for context.

  3. Two stations are interrogated for one message type each. Length is 160 bits. The second message type and second slot offset associated with the first queried MMSI should be zeroed.

  4. One station is interrogated for two message types, and a second for one message type. Length is 160 bits.

Type 16: Assignment Mode Command

Message type 16 is used by a base station with control authority to configure the scheduling of AIS informational messages from subordinate stations, either as a frequency per 10-minute interval or by specifying the TDMA slot(s) offset on which those messages should be transmitted. It is probably not of interest unless you are studying the internal operation of an AIS base station network. Length may be 96 or 144 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 16

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-69

30

Destination A MMSI

mmsi1

u

9 decimal digits

70-81

12

Offset A

offset1

u

See [IALA]

82-91

10

Increment A

increment1

u

See [IALA]

92-121

30

Destination B MMSI

mmsi2

u

9 decimal digits

122-133

12

Offset B

offset2

u

See [IALA]

134-143

10

Increment B

increment2

u

See [IALA]

If the message is 96 bits long, it should be interpreted as an assignment for a single station (92 bits) followed by 4 bits of padding reserved for future use. If the message is 144 bits long it should be interpreted as a channel assignment for two stations; no padding follows.

When increment is zero, the offset field is interpreted as the frequency with which the subordinate station should report per 10-minute interval. When increment is nonzero, reporting interval is specified at the level of TDMA slot numbers; see [IALA] for the detailed specification.

Note: While the 96-bit form of Type 16 is not uncommon, the 144-bit form is extremely rare. As of March 2010 it has not been observed even in long-duration samples from AISHub.

Type 17: DGNSS Broadcast Binary Message

Message type 17 is used to broadcast differential corrections for GPS. The data in the payload is intended to be passed directly to GPS receivers capable of accepting such corrections. 80 to 816 bits depending on payload size.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 17

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

Source MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-57

18

Longitude

lon

I1

Signed: minutes/10

58-74

17

Latitude

lat

I1

Signed: minutes/10

75-79

5

Spare

x

Not used - reserved

80-815

736

Payload

data

d

DGNSS correction data

Note that latitude and longitude are in units of a tenth of a minute; sign interpretation and out-of-band values are as in the Common Navigation Clock. (Note, however, that the hex representation of the out-of-band values differs; it is 181 \* 60 \* 10 = 0x1a838 for longitude, 91 \* 60 \* 10 = 0xd548 for latitude.)

The [IALA] description of the payload portion sub-fields has been omitted, as it appears to be tied to the now obsolete RTCM2 protocol.

Type 18: Standard Class B CS Position Report

A less detailed report than types 1-3 for vessels using Class B transmitters. Omits navigational status and rate of turn. Fields are encoded as in the common navigation block. 168 bits total.

In [IALA] (and [ITU1371]) bits 141-145 were designated "Spare"; the bit-flag semantics given here are from ITU-1371-3 and were communicated by Kurt Schwehr. Kurt warns that "the spec does not do a good job of explaining these fields…​ I don’t think that I totally understand these fields."

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 18

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

MMSI

mmsi

u

9 decimal digits

38-45

8

Regional Reserved

reserved

x

Not used

46-55

10

Speed Over Ground

speed

U1

As in common navigation block

56-56

1

Position Accuracy

accuracy

b

See below

57-84

28

Longitude

lon

I4

Minutes/10000 (as in CNB)

85-111

27

Latitude

lat

I4

Minutes/10000 (as in CNB)

112-123

12

Course Over Ground

course

U1

0.1 degrees from true north

124-132

9

True Heading

heading

u

0 to 359 degrees, 511 = N/A

133-138

6

Time Stamp

second

u

Second of UTC timestamp.

139-140

2

Regional reserved

regional

u

Uninterpreted

141-141

1

CS Unit

cs

b

0=Class B SOTDMA unit 1=Class B CS (Carrier Sense) unit

142-142

1

Display flag

display

b

0=No visual display, 1=Has display, (Probably not reliable).

143-143

1

DSC Flag

dsc

b

If 1, unit is attached to a VHF voice radio with DSC capability.

144-144

1

Band flag

band

b

Base stations can command units to switch frequency. If this flag is 1, the unit can use any part of the marine channel.

145-145

1

Message 22 flag

msg22

b

If 1, unit can accept a channel assignment via Message Type 22.

146-146

1

Assigned

assigned

b

Assigned-mode flag: 0 = autonomous mode (default), 1 = assigned mode.

147-147

1

RAIM flag

raim

b

As for common navigation block

148-167

20

Radio status

radio

u

See [IALA] for details.

The radio status is 20 bits rather than 19 because an extra first bit selects whether it should be interpreted as a SOTDMA or ITDMA state.

Type 19: Extended Class B CS Position Report

A slightly more detailed report than type 18 for vessels using Class B transmitters. Omits navigational status and rate of turn. Fields are encoded as in the common navigation block and the Type 5 message. Note that until just before the reserved field at bit 139 this is identical to message 18. 312 bits total.

In practice, the information in the ship name and dimension fields is not reliable, as it has to be hand-entered by humans rather than gathered automatically from sensors.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 19

6-7

2

Repeat Indicator

repeat

u

As in CNN

8-37

30

MMSI

mmsi

u

9 digits

38-45

8

Regional Reserved

reserved

u

46-55

10

Speed Over Ground

speed

U1

As in CNB.

56-56

1

Position Accuracy

accuracy

b

As in CNB.

57-84

28

Longitude

lon

I4

Minutes/10000 (as in CNB)

85-111

27

Latitude

lat

I4

Minutes/10000 (as in CNB)

112-123

12

Course Over Ground

course

U1

Relative to true north, units of 0.1 degrees

124-132

9

True Heading

heading

u

0 to 359 degrees, 511 = N/A

133-138

6

Time Stamp

second

u

Second of UTC timestamp.

139-142

4

Regional reserved

regional

u

Uninterpreted

143-262

120

Name

shipname

s

20 6-bit characters

263-270

8

Type of ship and cargo

shiptype

e

As in Message 5

271-279

9

Dimension to Bow

to_bow

u

Meters

280-288

9

Dimension to Stern

to_stern

u

Meters

289-294

6

Dimension to Port

to_port

u

Meters

295-300

6

Dimension to Starboard

to_starboard

u

Meters

301-304

4

Position Fix Type

epfd

e

See "EPFD Fix Types"

305-305

1

RAIM flag

raim

b

As in CNB.

306-306

1

DTE

dte

b

0=Data terminal ready, 1=Not ready (default).

307-307

1

Assigned mode flag

assigned

u

See [IALA] for details

308-311

4

Spare

x

Unused, should be zero

Type 20 Data Link Management Message

This message is used to pre-allocate TDMA slots within an AIS base station network. It contains no navigational information, and is unlikely to be of interest unless you are implementing or studying an AIS base station network. Length varies from 72-160 depending on the number of slot reservations (1 to 4) in the message.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 20

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-51

12

Offset number 1

offset1

u

Reserved offset number

52-55

4

Reserved slots

number1

u

Consecutive slots

56-58

3

Time-out

timeout1

u

Allocation timeout in minutes

59-69

11

Increment

increment1

u

Repeat increment

70-81

12

Offset number 2

offset2

u

Reserved offset number

82-85

4

Reserved slots

number2

u

Consecutive slots

86-88

3

Time-out

timeout2

u

Allocation timeout in minutes

89-99

11

Increment

increment2

u

Repeat increment

100-111

12

Offset number 3

offset3

u

Reserved offset number

112-115

4

Reserved slots

number3

u

Consecutive slots

116-118

3

Time-out

timeout3

u

Allocation timeout in minutes

119-129

11

Increment

increment3

u

Repeat increment

130-141

12

Offset number 4

offset4

u

Reserved offset number

142-145

4

Reserved slots

number4

u

Consecutive slots

146-148

3

Time-out

timeout4

u

Allocation timeout in minutes

149-159

11

Increment

increment4

u

Repeat increment

See [IALA] for details on the meaning of these fields.

Type 21: Aid-to-Navigation Report

Identification and location message to be emitted by aids to navigation such as buoys and lighthouses.

This message is unusual in that it varies in length depending on the presence and size of the Name Extension field. May vary between 272 and 360 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 21

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 digits

38-42

5

Aid type

aid_type

e

See "Navaid Types"

43-162 1

120

Name

name

t

Name in sixbit chars

163-163

1

Position Accuracy

accuracy

b

As in CNB

164-191

28

Longitude

lon

I4

Minutes/10000 (as in CNB)

192-218

27

Latitude

lat

I4

Minutes/10000 (as in CNB)

219-227

9

Dimension to Bow

to_bow

u

Meters

228-236

9

Dimension to Stern

to_stern

u

Meters

237-242

6

Dimension to Port

to_port

u

Meters

243-248

6

Dimension to Starboard

to_starboard

u

Meters

249-252

4

Type of EPFD

epfd

e

As in Message Type 4

253-258

6

UTC second

second

u

As in Message Types 1-3

259-259

1

Off-Position Indicator

off_position

b

See Below

260-267

8

Regional reserved

regional

u

Uninterpreted

268-268

1

RAIM flag

raim

b

As in CNB

269-269

1

Virtual-aid flag

virtual_aid

b

See Below

270-270

1

Assigned-mode flag

assigned

b

See [IALA] for details

271-271

1

Spare

x

Not used

272-360

88

Name Extension

t

See Below

According to [IALA], the aid type field has values 1-15 for fixed and 16-31 for floating aids to navigation. The detailed list is as follows:

Table 63. Navaid Types
Code Definition

0

Default, Type of Aid to Navigation not specified

1

Reference point

2

RACON (radar transponder marking a navigation hazard)

3

Fixed structure off shore, such as oil platforms, wind farms, rigs. (Note: This code should identify an obstruction that is fitted with an Aid-to-Navigation AIS station.)

4

Spare, Reserved for future use.

5

Light, without sectors

6

Light, with sectors

7

Leading Light Front

8

Leading Light Rear

9

Beacon, Cardinal N

10

Beacon, Cardinal E

11

Beacon, Cardinal S

12

Beacon, Cardinal W

13

Beacon, Port hand

14

Beacon, Starboard hand

15

Beacon, Preferred Channel port hand

16

Beacon, Preferred Channel starboard hand

17

Beacon, Isolated danger

18

Beacon, Safe water

19

Beacon, Special mark

20

Cardinal Mark N

21

Cardinal Mark E

22

Cardinal Mark S

23

Cardinal Mark W

24

Port hand Mark

25

Starboard hand Mark

26

Preferred Channel Port hand

27

Preferred Channel Starboard hand

28

Isolated danger

29

Safe Water

30

Special Mark

31

Light Vessel / LANBY / Rigs

The name field is up to 20 characters of 6-bit ASCII. If this field is full (has no trailing @ characters) the decoder should interpret the Name Extension field later in the message (no more than 14 6-bit characters) and concatenate it to this one to obtain the full name.

[IALA] describes bits 219-248 As "Dimension/Reference for Position", implying that it is vessel dimensions as in message type 5.

The Off-Position Indicator is for floating Aids-to-Navigation only: 0 means on position; 1 means off position. Only valid if UTC second is equal to or below 59.

The Virtual Aid flag is interpreted as follows: 0 = default = real Aid to Navigation at indicated position; 1 = virtual Aid to Navigation simulated by nearby AIS station.

If present, the Name Extension consists of packed six-bit ASCII characters followed by 0-6 bits of padding to an 8-bit boundary. The [IALA] description says "This parameter should be omitted when no more than 20 characters for the name of the A-to-N are needed in total. Only the required number of characters should be transmitted, i.e. no @-character should be used." A decoder can deduce the bit length of the name extension field by subtracting 272 from the total message bit length.

Type 22: Channel Management

This message is broadcast by a competent authority (an AIS network control base station) to set VHF parameters for an AIS coverage region. Length is 168 bits.

This message contains no navigational information, and is unlikely to be of interest unless you are implementing or studying an AIS base station network.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 22

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

MMSI

mmsi

u

9 decimal digits

38-39

2

Spare

x

Not used

40-51

12

Channel A

channel_a

u

Channel number

52-63

12

Channel B

channel_b

u

Channel number

64-67

4

Tx/Rx mode

txrx

u

Transmit/receive mode

68-68

1

Power

power

b

Low=0, high=1

69-86

18

NE Longitude

ne_lon

I1

NE longitude to 0.1 minutes

87-103

17

NE Latitude

ne_lat

I1

NE latitude to 0.1 minutes

104-121

18

SW Longitude

sw_lon

I1

SW longitude to 0.1 minutes

122-138

17

SW Latitude

sw_lat

I1

SW latitude to 0.1 minutes

69-98

30

MMSI1

dest1

u

MMSI of destination 1

104-133

30

MMSI2

dest2

u

MMSI of destination 2

139-139

1

Addressed

addressed

b

0=Broadcast, 1=Addressed

140-140

1

Channel A Band

band_a

b

0=Default, 1=12.5kHz

141-141

1

Channel B Band

band_b

b

0=Default, 1=12.5kHz

142-144

3

Zone size

zonesize

u

Size of transitional zone

145-167

23

Spare

x

Reserved for future use

The values of the channel_a and channel_b fields are ITU frequency designators for channels A and B. Normally these will be 2087 and 2088, the AIS 1 and AIS 2 frequencies of 87B (161.975 MHz) and 88B (162.025 MHz) respectively. Regional authorities may set different frequencies.

The txrx field encodes the same information as the 2-bit field txrx field in message type 23; only the two low bits are used.

The power bit instructs designated receivers which power level to use.

If the message is broadcast (addressed field is 0), the ne_lon, ne_lat, sw_lon, and sw_lat fields are the corners of a rectangular jurisdiction area over which control parameters are to be set. If it is addressed (addressed field is 1), the same span of data is interpreted as two 30-bit MMSIs beginning at at bit offsets 69 and 104 respectively.

Yes, the addressed bit is after the fields it controls the interpretation of.

Note that the 'not available' values for longitude and latitudes match the short ones used in message 17, not the long ones used in the common navigation block and elsewhere.

The band fields control channel bandwidth for channels A and B, and the zonesize field describes the size of the transition zone around the control jurisdiction. The semantics of these fields are complicated, controlling transmitter behavior as it moves between jurisdictions; see [IALA] for full details.

Type 23: Group Assignment Command

This message is intended to be broadcast by a competent authority (an AIS network-control base station) to set operational parameters for all mobile stations in an AIS coverage region. Length is 160 bits.

This message contains no navigational information, and is unlikely to be of interest unless you are implementing or studying an AIS base station network.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Unsigned Integer: 23

6-7

2

Repeat Indicator

repeat

u

As in Common Navigation Block

8-37

30

MMSI

mmsi

u

Unsigned Integer: 9 digits

38-39

2

Spare

x

Not used

40-57

18

NE Longitude

ne_lon

u

Same as broadcast type 22

58-74

17

NE Latitude

ne_lat

u

Same as broadcast type 22

75-92

18

SW Longitude

sw_lon

u

Same as broadcast type 22

93-109

17

SW Latitude

sw_lat

u

Same as broadcast type 22

110-113

4

Station Type

station_type

e

See "Station Types"

114-121

8

Ship Type

ship_type

e

See "Ship Types"

122-143

22

Spare

x

Not used

144-145

2

Tx/Rx Mode

txrx

u

See "Transmit/Receive Modes"

146-149

4

Report Interval

interval

e

See "Station Intervals"

150-153

4

Quiet Time

quiet

u

0 = none, 1-15 quiet time in minutes

154-159

6

Spare

x

Not used

The target set of mobile stations is specified by the station-type and ship-type fields. An addressed (non-broadcast) message 22 overrides a message 23, but a message 23 overrides a broadcast message 22.

Note that the 'not available' values for longitude and latitudes match the short ones used in messages 17 and 22, not the long ones used in the common navigation block and elsewhere.

The txrx field tells the affected stations which channel or channels they may transmit on. The options refer to the same A and B VHF channels as in Message Type 22. The field is interpreted as follows:

Table 64. Transmit Modes

0

TxA/TxB, RxA/RxB (default)

1

TxA, RxA/RxB

2

TxB, RxA/RxB

3

Reserved for Future Use
Table 65. Station Types

0

All types of mobiles (default)

1

Reserved for future use

2

All types of Class B mobile stations

3

SAR airborne mobile station

4

Aid to Navigation station

5

Class B shipborne mobile station (IEC62287 only)

6-9

Regional use and inland waterways

10-15

Reserved for future use

[INLAND] specifies 6 (only) as the station type value for inland waterways, reserving 7-9 for (other) regional uses.

Reporting Interval is a 4 bit unsigned integer, how often to report while within the area specified by this message. When the dual-channel operation is suspended by Tx/Rx mode command 1 or 2, the reporting interval is twice the interval given in the table.

Table 66. Station Intervals

0

As given by the autonomous mode

1

10 Minutes

2

6 Minutes

3

3 Minutes

4

1 Minute

5

30 Seconds

6

15 Seconds

7

10 Seconds

8

5 Seconds

9

Next Shorter Reporting Interval

10

Next Longer Reporting Interval

11-15

Reserved for future use

Quiet Time is a 4 bit unsigned integer specifying how many minutes affected stations are to remain silent. If a class B station receives a quiet time command, it will continue to schedule nominal transmission time periods, but is not to transmit message 18 or 24 during the quiet period.

Type 24: Static Data Report

Equivalent of a Type 5 message for ships using Class B equipment. Also used to associate an MMSI with a name on either class A or class B equipment.

A "Type 24" may be in part A or part B format; According to the standard, parts A and B are expected to be broadcast in adjacent pairs; in the real world they may (due to quirks in various aggregation methods) be separated by other sentences or even interleaved with different Type 24 pairs; decoders must cope with this. The interpretation of some fields in Type B format changes depending on the range of the Type B MMSI field. 160 bits for part A, 168 bits for part B.

According to the standard, both the A and B parts are supposed to be 168 bits. However, in the wild, A parts are often transmitted with only 160 bits, omitting the 'spare' 7 bits at the end. Implementers should be permissive about this.

[IALA] does not describe this message type; format information is thanks to Kurt Schwehr.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 24

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 digits

38-39

2

Part Number

partno

u

0-1

40-159

120

Vessel Name

shipname

t

(Part A) 20 sixbit chars

160-167

8

Spare

x

(Part A) Not used

40-47

8

Ship Type

shiptype

e

(Part B) See "Ship Types"

48-65

18

Vendor ID

vendorid

t

(Part B) 3 six-bit chars

66-69

4

Unit Model Code

model

u

(Part B)

70-89

20

Serial Number

serial

u

(Part B)

90-131

42

Call Sign

callsign

t

(Part B) As in Message Type 5

132-140

9

Dimension to Bow

to_bow

u

(Part B) Meters

141-149

9

Dimension to Stern

to_stern

u

(Part B) Meters

150-155

6

Dimension to Port

to_port

u

(Part B) Meters

156-161

6

Dimension to Starboard

to_starboard

u

(Part B) Meters

132-161

30

Mothership MMSI

mothership_mmsi

u

(Part B) See below

162-167

6

Spare

x

(Part B) Not used

If the Part Number field is 0, the rest of the message is interpreted as a Part A; if it is 1, the rest of the message is interpreted as a Part B; values 2 and 3 are not allowed.

Bits 48-89 are as described in ITU-R 1371-4. In earlier versions to 1371-3 this was one sixbit-encoded 42-bit (7-character) string field, the name of the AIS equipment vendor. The last 4 characters of the string are reinterpreted as a model/serial numeric pair. It is not clear that field practice has caught up with this incompatible change. Implementations would be wise to decode that but span in both ways and trust human eyes to detect when the final 4 characters of the string or the model and serial fields are garbage.

Interpretation of the 30 bits 132-162 in Part B is variable. If the MMSI at 8-37 is that of an auxiliary craft, the entry is taken to refer to a small attached auxiliary vessel and these 30 bits are read as the MMSI of the mother ship. Otherwise the 30 bits describe vessel dimensions as in Message Type 5.

According to [MMSI], an MMSI is associated with an auxiliary craft when it is of the form 98XXXYYYY, where (1) the '98' in positions 1 and 2 is required to designate an auxiliary craft, (2) the digits XXX in the 3, 4 and 5 positions are the MID (the three-digit country code as described in [ITU-MID]) and (3) YYYY is any decimal literal from 0000 to 9999.

Type 25: Single Slot Binary Message

Maximum of 168 bits (a single slot). Fields after the Destination MMSI are at variable offsets depending on that flag and the Destination Indicator; they always occur in the same order but some may be omitted.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 25

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 digits

38

1

Destination indicator

addressed

b

0=broadcast, 1=addressed.

39

1

Binary data flag

structured

b

See below

40

0/30

Destination MMSI

dest_mmsi

u

Message destination

?

0/16

Application ID

app_id

u

Unsigned integer

?

0-128

Data

data

d

Binary data

If the 'addressed' flag is on, 30 bits of data at offset 40 are interpreted as a destination MMSI. Otherwise that field span becomes part of the message payload, with the first 16 bits used as an Application ID if the 'structured' flag is on.

If the 'structured' flag is on, a 16-bit application identifier is extracted; this field is to be interpreted as a 10 bit DAC and 6-bit FID as in message types 6 and 8. Otherwise that field span becomes part of the message payload.

The data fields are not, in contrast to message type 26, followed by a radio status block.

Note: Type 25 is extremely rare. As of April 2011 it has not been observed even in long-duration samples from AISHub.

Type 26: Multiple Slot Binary Message

Takes up 60-1064 bits (up to 5 slots).

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 26

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 digits

38

1

Destination indicator

addressed

b

0=broadcast, 1=addressed.

39

1

Binary data flag

structured

b

See below

40

0/30

Destination MMSI

dest_mmsi

u

Message destination

?

0/16

Application ID

app_id

u

Unsigned integer

?

0-1004

Data

data

d

Binary data

?

20

Radio status

radio

u

See [IALA] for details.

The data field may span up to 5 256-bit slots in addition to the tail end of the base slot. The application_ID field, if present, is to be interpreted as a 10 bit DAC and 6-bit FID as in message types 6 and 8. Documentation says the data length of each slot is 224 and adds the note "Allows for 32 bits of bit-stuffing."

The 20 radio status bits are always present after end-of-data in the last slot and are in the format specified by [IALA]. The radio status is 20 bits rather than 19 because an extra first bit selects whether it should be interpreted as a SOTDMA or ITDMA state.

Note: Type 26 is extremely rare. As of April 2011 it has not been observed even in long-duration samples from AISHub.

Type 27: Long Range AIS Broadcast message

ITU-1371-4 says this message is primarily intended for long-range detection of AIS Class A equipped vessels (typically by satellite). This message has a similar content to Messages 1, 2 and 3, but the total number of bits has been compressed to allow for increased propagation delays associated with long-range detection

Length according to ITU-1374 is 96 bits. However, in the wild these are sometimes transmitted with 168 bits (a full slot). Robust decoders should warn when this occurs but decode the first 96 bits.

Field Len Description Member T Units

0-5

6

Message Type

type

u

Constant: 27

6-7

2

Repeat Indicator

repeat

u

As in CNB

8-37

30

MMSI

mmsi

u

9 decimal digits

38-38

1

Position Accuracy

accuracy

u

See Common Navigation Block

39-39

1

RAIM flag

raim

u

See Common Navigation Block

40-43

4

Navigation Status

status

u

See Common Navigation Block

44-61

18

Longitude

lon

I1

minutes/10 East positive, West negative 181000 = N/A (default)

62-78

17

Latitude

lat

I1

minutes/10 North positive, South negative 91000 = N/A (default)

79-84

6

Speed Over Ground

speed

u

Knots (0-62); 63 = N/A (default)

85-93

9

Course Over Ground

course

u

0 to 359 degrees, 511 = not available.

94-94

1

GNSS Position status

gnss

u

0 = current GNSS position 1 = not GNSS position (default)

95-95

1

Spare

x

Not used

Local extensions

Some regional authorities extend the AIS message set.

The St. Lawrence Seaway broadcasts hydrological and lock-scheduling messages using special encodings of the binary data of message types 6 and 8 (described in [SEAWAY], freely available), and safety information using types 12 and 14. These message types are listed under the description of type 8.

The U.S. Coast Guard has a system called PAWSS (Port and Water Safety System) which uses extended AIS binary formats. [SEAWAY] says it’s compatible with the St. Lawrence Seaway system and describes three PAWSS-specific messages in its Appendix A.

Since 2007 the Port Authority of London has operated a Thames AIS system covering the Thames River; it uses extensions of message types 6 and 8. It is describes in [THAMES].

Since 2006 there has been some effort to standardize inland-waterway extensions, described in [INLAND]. It uses different message formats and identifiers than the PAWS/St. Lawrence systems, which do not conform. There is an AIS extension called "RIS" (River Information System) that covers portions of the Danube River and Black Sea which does conform.

[IMO289] standardizes some subtypes of messages 6 and 8 similar to PAWSS messages for DAC 1, the international jurisdiction code. However, in some cases identically named subtypes are assigned different FIDs.

U.S. Coast Guard Extended AIVDM

You may occasionally see AIVDM packets with additional comma-separated fields following the checksum. This is a semi-obsolescent logging format used by the USCG, which has never documented it well and plans to replace it with a new one based on NMEA 4.0.

Here’s a sample sentence and field breakdown:

!AIVDM,1,1,,B,15Cjtd0Oj;Jp7ilG7=UkKBoB0<06,0*63,s1234,d-119,T12.34567123,r003669958,1085889680

Following the "*63" checksum are additional fields delimited by commas. These fields provide additional metadata about the reception of each AIS broadcast.

The field beginning with the lower case "s" is a Relative Signal Strength Indicator (RSSI) measurement from the receiver. This measurement has a range of 0-65535. This is one of the parameters used internally by the AIS receiver to determine the signal strength value as reported in the field beginning with the lower case "d". This field only exists when the AIS receiver provides this data.

The field beginning with a lower case "d" is the signal strength measurement for this broadcast in dBm. This field only exists when the AIS receiver provides this data.

The field beginning with the upper case "T" is the Time of Arrival of the received broadcast in seconds from UTC 0. This field only exists when the AIS receiver provides this data.

Another optional field not shown is one that begins with an upper case "S" and represents the slot number in which the reception occurred. The field would appear after the checksum and before the station identifier field. This field only exists when the AIS receiver provides this data. Example: S0042

The field beginning with the lower case "r" is a station identifier field. This field is always provided, regardless of the type of AIS equipment. (Occasionally a base station identifier will be prefixed with "b" instead.)

The last field is a time tag based on the standard C programming language time function. Both date and time to the nearest second can be derived from this field. This field is always provided, regardless of the type of AIS equipment.

NMEA Tag Blocks

Beginning with NMEA 4.10, the standard describes a way to intersperse "tag blocks" with AIS sentences in order to supply additional metadata, usually a Unix timestamp to be associated with a sentence (or contiguous group of sentences such as an armored AIS Type 5).

The tag block facility is complex, in some respects poorly specified, and there has not yet been much public discussion of it. This section should be considered provisional and in need of improvement.

The general format of a tag block is: an opening backslash, followed by multiple comma-separated fields none of which may contain backslashes, followed by an asterisk and NMEA checksum, followed by a closing backslash.

The following is an example of an AIS Type 1 sentence preceded by a tag block:

\g:1-2-73874,n:157036,s:r003669945,c:1241544035*4A\!AIVDM,1,1,,B,15N4cJ`005Jrek0H@9n`DW5608EP,0*13

Each comma-separated field is expected to be a type key, followed by a colon, followed by content. The semantics of the type keys are as follows:

Confusingly, there is a different standard introduced with NMEA 4.00, IEC 62320-1, that uses the same tag block format but a slightly different (overlapping) set of field keys

Table 67. NMEA 4.00 Field Types
IEC NMEA Type Description

c

c

int>0

UNIX time in seconds or milliseconds

d

d

string

Destination (at most 15 chars)

xGy

g

int-int-int

Sentence grouping

x

n

int>0

line count

r

int>0

relative time

s

s

string

Source / station

i

t

string

Text string (at most 15 chars)

The IEC 62320-1 and NMEA 4.10 c field is an emission time for the sentence it precedes. We’re not yet sure what the time unit is.

The NMEA 4.10 g value describes a sentence or sentence group to associate the tag block to. It is a triple of ints separated by dashes. The first number is the sentence number, the second is total number of sentences to make up one group. The third number is an identifier for that particular group. If there is no g value, the tag block simply applies to the following sentence.

As of May 2014 no NMEA 4.10 relative time fields have been observed in the wild. It is unknown whether the unit is seconds or milliseconds.

The d, i/t, and s fields are intended to be used for filtering by station IDs included in them.

Part of the NMEA 4.10 standard describes a configuration message facility by which AIS message receivers can send queries to AIS senders, and under some circumstances change the semantics if tag blocks (in particular, by specifying time units and epoch).

We do not yet have more definite information on the meaning of these fields or how they are related to nearby AIVDM/AIVDO sentences. We hope to add this in a future revision.

AIS Payload Byte Alignment, Padding, and Bit Stuffing

Warning: Here there be dragons. Read with care. Once you get through it, you will at least not encounter anything more confusing in the rest of this document.

Byte Alignment

AIS is a bit-sync protocol. While some fields within AIS payloads are 8-bit-byte-aligned with preceding padding, most are not. Furthermore, while most message variants have bit lengths that are a multiple of 8, some do not.

[ITU1371] includes a single sentence, easy to miss, requiring over-the-air messages to have trailing padding to a 8-bit boundary. In most cases message lengths are a multiple of 8 with trailing spare fields added to ensure this; thus, the requirement will not change the transmitted bitlength of the message from what’s described in the standard. There are, however, two exceptions to this rule.

One is an apparent error in the format design. The type 15 message has a variant with 108 data bits and a trailing 2-bit spare field, for 110. This spare should have been 4 bits to guarantee a byte boundary at 112 bits. Decoders need to be prepared to encounter this length in case the transmitter has implemented the padding requirement properly.

The other is messages containing variable-length text packed into 6-bit nibbles: types 6, 12, and 14. They may have trailing padding after the last nibble to get to an 8-bit boundary. Decoders should be prepared to encounter and ignore this.

The variable-length binary message types 8, 17, 25, and 26 are constrained to have data payloads of a size such that the payload ends on a byte boundary, but should not require special handling on this account. The binary data in message types 8 and 17 is also guaranteed to begin on a byte boundary, but this is not true of the addressed variants of type 25 and 26.

Interaction with AIVDM padding

AIVDM armoring introduces a second layer of padding, with confusing consequences. The real payload, already padded to a bit length that is a multiple of 8 by the AIS radio layer, gets armored as a sequence of ASCII characters encoding 6-bit nibbles. To capture all of it, the payload must in effect be padded to the next multiple of 6.

Consider a type 12 message with 5 sixbit characters in it. These will become bits 72-102 in the over-the-air message. The AIS radio layer will pad that to 104 bits at transmission to get to an 8-bit boundary. The receiver, reporting the data in AIVDM armoring, will pad that to 108 bits to get to a 6-bit boundary, encode the result, and issue a pad character of '4' to indicate that the low 4 bits of the last 6-bit nibble should be ignored.

Because these requirements are tricky and poorly documented in the official standards, receivers not uncommonly get them wrong. The most common way to get them wrong seems to be by computing the pad character incorrectly.

The most common error observed in the wild on AISHub is reporting a pad 2 bits too small, making the message look like it is 2 bits longer than it actually is. This seems for some reason to be most common on Type 5 messages, which then decode as 426 bits rather than 424.

Accordingly, we recommend that when validating fixed-size messages by type and bit-length, decoders should accept messages that are up to 5 bits over their theoretically correct length.

For messages with a variable-length trailing payload (6, 8, 12, 14, 17, 25, 26) there is no way to detect that the pad character might be wrong. If it is, this will manifest as truncation of the last nibble or extra trailing zero data.

Bit Stuffing

The following probably will not affect decoders. Nevertheless, we document it here because it is just the sort of thing that is (a) likely to confuse implementors reading the public portions of the standards, and (b) all too likely to become visible if there are firmware or software errors in the transmission chain.

There are references to "bit-stuffing" in the [IALA] clarifications describing certain payload fields. [C2] reveals the following in 3.2.2.1: "The bitstream is subject to bit stuffing. This means that if more than 5 consecutive 1s are found in the output bit stream, a zero is inserted. This applies to all bits except the databits of HDLC flags." [IALA] clarifies as follows: "On the transmitting side, this means that if five (5) consecutive ones (1s) are found in the output bit stream, a zero should be inserted after the five (5) consecutive ones (1s). This applies to all bits between the HDLC flags […​] On the receiving side, the first zero after five (5) consecutive ones (1s) should be removed."

It appears that this bit stuffing is meant to be performed by the AIS radio link layer at transmission time and undone at reception time, and should not be visible in AIVDM payloads reported by the receiver.

AIS feed sites

Most sites that advertise "live" AIS feeds actually give you a map display through a browser. Here are a few from which you can get raw sentence data over a TCP/IP port for testing. Coverage on these is not yet very comprehensive; these sites tend to have good coverage in Europe, the U.S. and a few ports in Asia but to be spotty elsewhere. See their siting maps for details.

  • AIS Hub: Share alike. You contribute a feed, you get back all feeds.

  • AIS Live: Subscription access to real-time data. No longer has free access even to delayed data.

JSON-AIS encoding

Here is an application of the JSON metaformat to present AIS data in a form more convenient for application use than AIVDM/AIVDO sentences. This encoding is implemented by GPSD and its client libraries. It is described here because (a) the specification is closely tied to the field encodings, and (b) the author wishes to offer it as an interoperability standard for other applications.

One previous effort, JSON-AIS, has been made to define a JSON-based standard for exchange of unpacked, human-readable AIS data. The latest version at time of writing, from December 2008,covers only a small subset of the most common AIS messages, and many data fields in the messages it does dump are omitted. Online links to the project have disappeared as of June 2023. The member names given in the bit-field tables match the attributes used in HAM-JSON-AIS when HAM-JSON-AIS includes that field.

The general ground rules for JSON-AIS encoding are as follows:

  1. Each sentence decodes to a JSON object.

  2. When multiple kinds of JSON objects may occur in a data stream, AIS objects have the attribute "class":"AIS".

  3. Some collections of fields aggregating to a timestamp are dumped in ISO8601 format.

Table 68. Timestamp fields
Message ITU/IMO fields JSON ISO8601 Format

4

year,month,day,hour,minute,second

timestamp

%4u-%02u-%02uT%02u:%02u:%02uZ

5

month,day,hour,minute

eta

%02u-%02uT%02u:%02uZ

6(1/12)

lmonth,lday,lhour,lminute

departure

%02u-%02uT%02u:%02uZ

nmonth,nday,nhour,nminute

eta

%02u-%02uT%02u:%02uZ

6(1/18)

month,day,hour,minute

arrival

%02u-%02uT%02u:%02uZ

6(1/20)

month,day,hour,minute

arrival

%02u-%02uT%02u:%02uZ

6(1/23)

month,day,hour,minute

timestamp

%02u-%02uT%02u:%02uZ

6(1/28)

month,day,hour,minute

start

%02u-%02uT%02u:%02uZ

8(1/11)

day,hour,minute

timestamp

%02uT%02u:%02uZ

8(1/11)

day,hour,minute

timestamp

%02uT%02u:%02uZ

8(1/13)

fmonth,fday,fhour,fminute

from

%02u-%02uT%02u:%02uZ

8(1/13)

tmonth,tday,thour,tminute

to

%02u-%02uT%02u:%02uZ

8(1/22)

month,day,hour,minute

timestamp

%02u-%02uT%02u:%02uZ

8(1/27)

month,day,hour,minute

start

%02u-%02uT%02u:%02uZ

8(200/23)

year,month,day,hour,minute

start

%4u-%02u-%02uT%02u:%02u

8(200/23)

year,month,day,hour,minute

end

%4u-%02u-%02uT%02u:%02u

  1. There are two variants of the encoding, one scaled and one unscaled, which differ in the treatment of float and controlled-vocabulary fields. An AIS-JSON object may have the optional attribute "scaled":true to signify that the rest of its fields are scaled; if this attribute has the value 'false' or is omitted, no scaling has been performed. Message types for which the unscaled and scaled dumps will differ are 1-5, 9, 11, 17-19, 21-24, and 27.

  2. In unscaled mode, float-valued fields are dumped in their unscaled integer form. In scaled mode, division or other specified scaling is applied and the value dumped as a float, except that certain extreme or data-unavailable value as may be dumped as fixed strings; see the table below.

  3. Each field in the Controlled Vocabularies list in the following table is dumped twice: once with its base name as an integer, once with "_text" appended to the name and the vocabulary item as value. (This behavior is new in GPSD protocol version 3.9; older versions made integer or string display dependent on the "scaled" flag.)

Table 69. Special fields
Message Float Fields Controlled Vocabularies

1-3

turn, speed, lon, lat

status

4, 11

lon, lat

epfd

5

draught

shiptype, epfd

6(1/14)

lon, lat, cspeed

-

6(1/18)

lon, lat

-

6(1/20)

berth_lon, berth_lat, berth_depth

position

6(1/22)

lon, lat

-

6(1/25)

code

code*

6(1/28)

lon, lat

rtype

6(1/32)

lon, lat, cspeed

-

6(235/100)

-

racon, light

8(1/11)

lon, lat, airtemp, dewpoint,

preciptype, ice

visibility, waterlevel, cspeed,

cspeed2, cspeed3, waveheight,

swellheight, watertemp salinity

8(1/17)

lon, lat

idtype*

8(1/18)

lon, lat

-

8(1/19)

-

signal, nextsignal

8(1/21)

lon, lat, visibility, airtemp,

-

watertemp, waveheight,

swellheight, speed, pressure, pdelta,

rwindspeed, mgustspeed, airtemp,

surftemp, cloudbase,

swheight1, swheight2

8(1/22)

lon, lat

-

8(1/25)

-

iceclass*

8(1/27)

lon, lat

rtype

8(1/31)

lon, lat, airtemp, dewpoint,

preciptype

visibility, waterlevel, cspeed,

cspeed2, cdepth2, cspeed3,

cdepth3, waveheight,

swellheight, watertemp, salinity

9

lon, lat, course

-

17

lon, lat

-

18

lon, lat, course

-

19

lon, lat, course

shiptype, epfd

21

lon, lat

aid_type, epfd

22-23

ne_lon,ne_lat, sw_lon, sw_lat

shiptype,stationtype

24

-

shiptype

27

lon, lat

-

This table does not include fields that are scaled by multipliers to integers. These are reported in the multiplied form in both scaled and unscaled modes.

Asterisked fields are not yet decoded by GPSD, but probably will be in a future release.

As the Beaufort scale is usually quoted numerically, conforming implementations should do so rather than expanding to its controlled vocabulary.

Table 70. String special values in scaled mode
Message Fieldname Special values

1-3

turn

"nan" = not available, "fastright" = fast right turn (above 5deg/30sec degrees), "fastleft" = fast left turn (above 5deg/30sec degrees).

1-3

speed

"nan" = not available, "fast" = speed >= 102.2 knots

9

alt

"nan" = not available, "high" = alt >= 4094 meters

9

speed

"nan" = not available, "fast" = speed >= 1023.0 knots

  1. Trailing arrays are dumped as JSON subobject arrays. The name of the array item is the name given in the 'a' table entry. Explicit array count fields (presently "waycount" in Route Info messages") are not dumped.

  2. In the VTS-Generated/Synthetic Targets message, the id field is dumped as the value of an attribute the name of which is specified by the idtype field.

Open Questions

The AIS standards are not marvels of clear and unambiguous drafting. We list here some open questions which could usefully be addressed by governing authorities.

Some of these duplicate material in paragraphs tagged with OPEN-QUESTION. They are collected here for convenience.

The message type summary table in [INLAND] indicates the existence of a broadcast (unaddressed) variant of Inland Number of Persons On Board. But no field breakdown is given for this variant. If it supposed to be identical to the Type 6 layout, what is to be done with the Destination MMSI field?

Are [INLAND] time-of-day fields UTC or local?

In [INLAND] RTA at lock/bridge/terminal message, no default is specified for the Status field.

In Inland Ship Static and Voyage Related Data, which of two possible ERI numeric codesets are used for the Type field - the 4-digit codes in the 8000-8073 range, or the AIS codes in the 1-99 range? Full ERI codes have been observed in the wild.

In the [INLAND] description of Message 5 extensions, footnote 6 is incomprehensible and not actually referenced in the table.

In the [INLAND] EMMA Warning and Signal Strength messages, the description is not explicit about the interpretation of the longitude and latitude fields; these semantics are assumed here from 28 and 27-bit fields in other messages.

In the [INLAND] EMMA Warning, what are the semantics of the min and max values? To what parameters do they apply?

Is the [IMO236] versions of Persons On Board, which is supposed to be Type 6 and thus addressed, erroneous? There is no destination address field in the layout.

[IMO289] says of the "VTS Generated/Synthetic Targets" message: "When MMSI or IMO number is used, the least significant bit should equal bit zero of the Target Identifier." It is unclear how "bit zero" is to be interpreted, but it is not possible to reconcile interpreting it as the leading bit of the field with AIS big-endian encoding. Settling this awaits live testing.

References

Change history

Version 1.0 was the initial release covering messages 1-3, 4, and 5.

Version 1.1 adds message breakdowns for 9 and 18, explanation of the Repeat Indicator field, and the explanation of USCG extended AIVDM.

Version 1.2 adds information on the ITU1371 edition 3 maneuver field, and the RAIM flag. It also adds an important clarification about six-bit decoding.

Version 1.3 adds information on message types 6, 7, 12, and 13, and attempts to demystify bit-stuffing.

Version 1.4 adds explicit decoding tables for ASCII armoring and six-bit ASCII.

Version 1.5 corrects the interpretation of field 7 in AIVDM ASCII-armored sentences.

Version 1.6 corrects some minor errors in the interpretation of Type 5 messages.

Version 1.7 adds descriptions for Type 10, 11, 19, 21, and 24 messages, information about ITU-1371-3 flags in message type 18, and the new section on Improving This Document.

Version 1.8 fixes some broken markup and adds information about JSON-AIS.

Version 1.9 adds more information on JSON and the member names.

Version 1.10 fixes a typo in the formula for undoing 6-bit armoring.

Version 1.11 describes message types 15, 16, and 17.

Version 1.12 describes messages 20 and 22, and adds navigation aid type codes.

Version 1.13 documents more out-of-band values and treats radio status blocks more uniformly.

Version 1.14 documents message 23.

Version 1.15 corrects an incorrect member name in message 5. It didn’t match my C code, but had no effect on conformance with the standard. I corrected it because it confused someone working on a Python decoder.

Version 1.16 incorporated various minor fixes and corrections from Neal Arundale. One 'standard' fieldname changed, in message type 21: type → aid_type.

Version 1.17 clarifies the role of @ as a terminator in 6-bit text.

Version 1.18 notes a possible off-by-two error in the standards' description of type 14, and noted that type 25 and 26 have not been observed in the wild. It also adds a more complete description of AIS data types and some pragmatics about spare and reserved fields.

Version 1.19 adds a description of AIS Hub.

Version 1.20 adds a list of AIS feed sites - just two, so far.

Version 1.21 describes JSON-AIS more completely. It adds descriptions for AIS messages type 25 and 26, not yet observed in the wild.

Version 1.22 describes the problem with message length checks. Notes on EPFD value 15 and shiptype values > 99 are added. Added another AIS feed. Corrections and more details on message 22.

Version 1.23 corrects some typos and numbering errors in the description of message 19 (field widths were correct, though). Also, AISLive no longer offers free delayed access.

Version 1.24 breaks the Type 6 and 8 application_id field into DAC and FID and adds tables for known DAC/FID pairs and their sources. Unspecified fields are now omitted in JSON dumps. A new section "AIS byte alignment, bit stuffing, and padding", reveals some particularly black magic.

Version 1.25 adds clarifications and more message subtypes for U.S. Coast Guard PAWSS messages.

Version 1.26 corrects an error in describing rate-of-turn decoding in AIS Type 1, 2, and 3 messages,

Version 1.27 describes the sometime U.S. practice of omitting the leading '3' region code from MMSIs.

Version 1.28 merges updates from IMO289, communicated by Kurt Schwehr.

Version 1.29 added much information on WMO special message formats in types 6 and 8.

Version 1.30 was revised because M.1371-4 is now a free download. Also, we describe "pilot plugs" and AIS message type 27. We get much more explicit about defaults in IMO236 and IMO289 messages.

Version 1.31 shortened some C names in the Meteorological/Hydrological messages and fixed typos.

Version 1.32 adds descriptions of IMO Area Notice and Environmental messages. It adds explicit type information to the tables.

Version 1.33 notes that the home location of "NMEA Revealed" became unstable in late 2011.

Version 1.34 fixes a typo in the MMSI 2 field offset of message 7.

Version 1.35 notes that 24A and 24B messages don’t necessarily come in neat adjacent pairs and that decoders need to handle this.

Version 1.36 corrects erroneous scale factors in the IMO289 Area Notice and Time to Enter Port descriptions.

Version 1.36 adds breakdowns of Aid to Navigation monitoring messages used in the UK and the Republic of Ireland.

Version 1.37 corrects a field signedness error in the IMO236 and IMO289 Met/Hydro messages.

Version 1.38 corrects a minor bug in the description of the Navigation Message ROT field. Adds information on AIS-SART.

Version 1.39 corrects signedness errors in the description of the Air Temperature and Water Temperature fields in the IMO289 Weather Report From Ship message.

Version 1.40 notes that AIS channel codes '1' and '2' may be encountered in the wild.

Version 1.41 has been slightly amended because type 27s have started showing up on satellite feeds.

Version 1.42 fixes a typo in the Type 4 message description.

Version 1.43 describes the ITU-R 1371-4 breakdown of the Type 24 Vendor ID field and adds information on AIS standards for inland waterways. Also Inland AIS standard messages are now covered.

Version 1.44 adds substantial new information on MMSIs and updates the [MMSI] link, which was stale.

Version 1.45 adds a description of variant AIS talker IDs and NMEA 4.10 tag blocks.

Version 1.46 corrects an error in the specification on Inland AIS Type 10s. It also adds a bit more information on AIS tag blocks.

Version 1.47 corrects some minor field type errors in Type 18 and Type 19 speed fields. Also corrected Type 9 radio field length.

Version 1.48 corrects two typos in the WMO289 Area Notice and Weather Report From Ship definitions.

Version 1.49 adds a technical detail about non-AIS encapsulated sentences.

Version 1.50 fixes a couple of typos in the ISO289 Berthing Data and Tidal Window message descriptions.

Version 1.51 fixes an incorrect bit length in the IMO289 Hydrological Data message.

Version 1.52 fixes many small typos. Change Gratipay to Patreon.

Version 1.53 fixes several small typos and formatting errors, adds detail to the Types 6 and 8 Area Notice message, and adds reference to the IALA Application-Specific Message (ASM) registry.

Version 1.54 adds information on subarea fields in IMO289 Area Notice messages.

Version 1.55 add Table of Contents. Markup cleanup.

Version 1.56 fix typos per Jim J. Jewett

Version 1.57 Update Type 1/2/3 Nav Statusa, and EPFD, Descriptions. Fix dead link to [MSGS123].

Version 1.58 Fix many dead links