How many AIS message types are there?

There are 27 AIS message types defined in the ITU-R M.1371 standard. These include position reports (Types 1-3, 18, 19, 27), static data (Types 5, 24), safety messages (Types 12-14), and various system management messages.

What is AIS Message Type 1?

AIS Message Type 1 is a scheduled position report from Class A shipborne mobile equipment. It contains navigation status, rate of turn, speed over ground, position, course over ground, heading, and timestamp. It is transmitted every 2-10 seconds based on vessel speed.

What is the difference between Class A and Class B AIS?

Class A AIS is mandatory on SOLAS vessels and transmits more frequently (every 2-10 seconds) at higher power (12.5W). Class B AIS is for smaller vessels, transmits every 30 seconds to 3 minutes at 2W, and has limited message type support.

What data is in AIS Message Type 5?

AIS Message Type 5 contains static and voyage data: IMO number, call sign, ship name, ship type, dimensions, draught, destination, and ETA. It is transmitted every 6 minutes or on request.

AIS Technical Reference

AIS Message Types

A complete guide to all 27 AIS message types, their purposes, transmission frequencies, and the data they contain.

Message Types

Position Reports

Static Data

Safety Messages

Understanding AIS Messages

AIS (Automatic Identification System) uses a standardized set of 27 message types to transmit different kinds of maritime information. Each message type serves a specific purpose and is transmitted at defined intervals.

Messages are organized into categories: position reports for real-time tracking, static and voyage data for vessel identification, safety messages for maritime safety communications, and other messages for system management and specialized applications.

Position Reports

Static/Voyage Data

Safety Messages

Other Messages

Most Common Message Types

These message types make up the majority of AIS traffic you'll encounter.

Types 1, 2, 3

Class A Position Report

The most common AIS messages. Transmitted by Class A transponders on large commercial vessels every 2-10 seconds depending on speed.

Data Included:

PositionSpeedCourseHeadingTurn RateNav Status

Type 5

Static and Voyage Data

Contains vessel identification and voyage information. Transmitted every 6 minutes or when requested.

Data Included:

IMO NumberShip NameCall SignShip TypeDimensionsDestinationETADraught

Type 18

Class B Position Report

Position report from Class B transponders on smaller vessels. Less frequent updates than Class A.

Data Included:

PositionSpeedCourseHeading

Type 21

Aid to Navigation Report

Position and status from navigation aids like buoys, lighthouses, and markers.

Data Included:

AtoN TypePositionNameDimensionsStatus

Complete Message Type Reference

Full list of all 27 AIS message types with their specifications.

Position Reports

Type	Name	Frequency	Description
1	Position Report (Class A)	2-10 seconds (based on speed)	Scheduled position report from Class A shipborne mobile equipment. The most common message type.
2	Position Report (Class A)	2-10 seconds	Same as Type 1, but assigned to specific navigation status.
3	Position Report (Class A)	On interrogation	Same as Type 1, but used for response to interrogation.
9	SAR Aircraft Position Report	Every 10 seconds	Position report from search and rescue aircraft.
18	Position Report (Class B)	Every 30 seconds (moving) or 3 minutes (stationary)	Standard position report from Class B shipborne equipment.
19	Extended Position Report (Class B)	Every 3 minutes	Extended Class B position report with ship particulars.
21	Aid-to-Navigation Report	Every 3 minutes	Position report from aids to navigation (buoys, lighthouses).
27	Position Report (Long Range)	Every 3 minutes	Position report for long-range AIS (satellite detection).

Static and Voyage Data

Type	Name	Frequency	Description
5	Static and Voyage Data	Every 6 minutes or on request	Vessel static data and voyage-related information. Contains ship particulars.
24	Class B Static Data	Every 6 minutes	Static data report from Class B stations (Part A and Part B).

Safety Messages

Type	Name	Frequency	Description
12	Addressed Safety Message	As needed	Safety-related text message addressed to a specific station.
13	Safety Acknowledge	On receipt	Acknowledgement of addressed safety message.
14	Safety Broadcast Message	As needed	Broadcast safety-related text message to all stations.

System and Binary Messages

Type	Name	Frequency	Description
4	Base Station Report	Every 10 seconds	Position report from base stations. Used for reference points and navigation aids.
6	Binary Addressed Message	As needed	Addressed binary message for application-specific data exchange.
7	Binary Acknowledge	On receipt	Acknowledgement of received addressed binary messages.
8	Binary Broadcast Message	As needed	Broadcast binary message for area-specific information.
10	UTC/Date Inquiry	As needed	Request for UTC/date information.
11	UTC/Date Response	On request	Response to UTC/Date inquiry with current time.
15	Interrogation	As needed	Used to request a specific message type from another station.
16	Assignment Mode Command	As needed	Command to assign reporting parameters to Class A or B stations.
17	DGNSS Broadcast Binary Message	As needed	DGNSS corrections broadcast by base stations.
20	Data Link Management	As needed	Reserve TDMA slots for base station transmissions.
22	Channel Management	As needed	Manage regional channel configurations.
23	Group Assignment Command	As needed	Assign parameters to a group of stations in an area.
25	Single Slot Binary Message	As needed	Short binary message that fits in a single slot.
26	Multiple Slot Binary Message	As needed	Binary message with more payload capacity.

Class A vs Class B Transponders

AIS equipment comes in two main classes, each with different capabilities.

Class A

Required on SOLAS vessels (300+ GT international, passenger ships). Higher power, more frequent transmission.

Updates every 2-10 seconds
12.5W transmission power
Full message type support
Rate of turn data

Class B

Voluntary for smaller vessels. Lower cost, reduced functionality, but still provides essential tracking.

Updates every 30 seconds - 3 minutes
2W transmission power
Limited message types (18, 19, 24)
No rate of turn data

Access AIS Data via API

Get real-time vessel positions, historical tracks, and static data from all AIS message types through our REST API.

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AIS Message Types

Understanding AIS Messages

Most Common Message Types

Class A Position Report

Static and Voyage Data

Class B Position Report

Aid to Navigation Report

Complete Message Type Reference

Position Reports

Static and Voyage Data

Safety Messages

System and Binary Messages

Class A vs Class B Transponders

Class A

Class B

Related Resources

AIS Data Explained

MMSI Numbers

Navigation Status

Vessel Location API

Access AIS Data via API