Automatic Identification System (AIS) is a vital component of modern maritime navigation, enabling ships, shore stations, and navigation aids (AtoN) to communicate essential data wirelessly. One of the most important aspects of AIS technology is its ability to transmit structured messages—each carrying a specific type of navigational or identification data.
In this article, we break down AIS message types, their functions, and how they are used in both vessel communications and AtoN (Aid to Navigation) applications.
What Are AIS Message Types?
AIS messages are digital transmissions that carry structured maritime information. Each message consists of three key elements:
- MMSI (Maritime Mobile Service Identity): The unique ID of the transmitter (e.g., vessel, base station, buoy).
- Message ID: A code that identifies the type of message being transmitted.
- Repeat Indicator: Used to manage retransmissions, especially over obstacles.
These messages are automatically broadcast and received over VHF radio frequencies, allowing vessels and stations to share navigation, safety, and environmental data in real-time.
Full List of AIS Message Types and Their Functions
Below is a summary of all currently used AIS message types, categorized by their function and relevance:
| Message ID |
Name |
Function |
Notes |
| 1, 2, 3 |
Position Reports (Class A) |
Transmit vessel location, heading, speed, and navigational status. |
Sent every few seconds. |
| 4 |
Base Station Report |
Identifies shore station location and time. |
Provides static reference for vessels. |
| 5 |
Static and Voyage Data |
Reports vessel dimensions, draft, destination. |
Manually entered. |
| 6 |
Addressed Binary Message |
Custom data between two specific devices. |
For proprietary use. |
| 7 |
Binary Acknowledgement |
Confirms receipt of Message 6. |
|
| 8 |
Binary Broadcast Message |
Broadcast custom binary data to all. |
|
| 9 |
SAR Aircraft Position Report |
For search and rescue aircraft. |
Includes altitude. |
| 10 |
UTC/Date Inquiry |
Requests time/date from base station. |
Often triggered by GPS lack. |
| 11 |
UTC/Date Response |
Replies to Message 10. |
Same as Message 4. |
| 12 |
Safety-Related Message (Addressed) |
Sends short text to a specific vessel. |
Free-text or encoded. |
| 13 |
Safety-Related Acknowledgement |
Confirms Message 12 receipt. |
|
| 14 |
Safety Broadcast Message |
Public safety announcement. |
Broadcast to all. |
| 15 |
Interrogation |
Used to request information from other AIS units. |
By base stations. |
| 16 |
Assigned Mode Command |
Manages slot allocations. |
For timeslot coordination. |
| 17 |
GNSS Binary Broadcast |
Sends GPS differential corrections. |
Broadcast by base stations. |
| 18 |
Class B Position Report |
For Class B transponders (smaller vessels). |
Limited data compared to Class A. |
| 19 |
Extended Class B Report |
Includes more vessel data. |
Superseded by Msg 18. |
| 20 |
Data Link Management |
Allocates TDMA slots across network. |
Base station use. |
| 21 |
AtoN Report |
Transmitted by Aids to Navigation. |
Includes position, type, and condition. |
| 22 |
Channel Management |
Changes working VHF frequencies. |
For local coordination. |
| 23 |
Group Assignment Command |
Assigns parameters to multiple stations. |
Broadcast by authorities. |
| 24 |
Static Data (Class B) |
Class B vessel info similar to Msg 5. |
Sent in two parts (A/B). |
| 25 |
Single Slot Binary Message |
One-slot custom data. |
Efficient, low-overhead. |
| 26 |
Multi-Slot Binary Message |
Supports communication status field. |
For larger data payloads. |
| 27 |
Long-Range AIS Broadcast |
Satellite detection of vessels. |
Modified Msg 1/2/3 for satellite use. |
The Role of AIS AtoN in Modern Maritime Navigation
AIS Aids to Navigation (AtoN) are specially designed units that broadcast Message 21 to represent non-vessel objects such as buoys, light towers, and offshore platforms. These devices improve maritime safety by:
- Broadcasting fixed positions and unique IDs.
- Reporting environmental data (e.g., tide, current, or weather).
- Enabling remote monitoring of light status, battery condition, or sensor activity.
- Transmitting alerts for malfunction or drift.
AIS AtoN can be installed on shore (e.g., lighthouses) or offshore (e.g., buoys), and many are solar-powered with integrated GPS, making them autonomous and low-maintenance.
Why Understanding AIS Message Types Matters
Whether you're a ship operator, port authority, or equipment manufacturer, understanding AIS message types helps:
- Ensure compliance with IALA standards.
- Interpret messages correctly from AIS software or monitoring platforms.
- Design and deploy AIS-based AtoN systems with optimized data functionality.
For product manufacturers and system integrators, precise knowledge of AIS messages allows better planning of communication protocols and system capabilities.
Final Thoughts
AIS continues to revolutionize maritime safety, enabling real-time, standardized communication between ships, authorities, and navigation aids. The structured nature of AIS message types is fundamental to this ecosystem—each message serving a specific role in safe and efficient navigation.
If you're integrating AIS into your products, such as AIS-equipped buoys or solar navigation lanterns, ensure compatibility with relevant AIS message protocols and certifications (such as IALA compliance).
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