AIS message type
AIS message type 24: Static data report (Class B)
A Class B vessel's name (part A) and type, call sign and dimensions (part B). What type 24 carries, who sends it, how often, and how to read it.
What type 24 is
Class B units send static data in two one-slot parts. Part A, identified by a part number of 0, holds the 20-character name. Part B, with part number 1, holds ship and cargo type, vendor ID, call sign and either the four reference-point dimensions or, for an auxiliary craft such as a tender, the MMSI of its mother ship.
How to read it
The two parts are separate transmissions, so a receiver can hold a Class B name without a type, or a type without a name. A sender whose MMSI begins 98 is a craft associated with a parent ship, and part B then carries the parent's MMSI where the dimensions would be.
Field layout
Bit offsets are counted from zero at the first bit of the decoded payload.
| Bits | Field | Notes |
|---|---|---|
| 0–5 | Message type | |
| 6–7 | Repeat indicator | 0 = original, 1 to 3 = repeated by a repeater; 3 means do not repeat |
| 8–37 | MMSI | |
| 38–39 | Part number | 0 = part A, 1 = part B |
| 40–159 | Part A: vessel name | 20 six-bit characters |
| 40–47 | Part B: ship and cargo type | |
| 48–65 | Part B: vendor ID | 3 six-bit characters, then a 4-bit unit model code and 20-bit serial number |
| 90–131 | Part B: call sign | 7 six-bit characters |
| 132–140 | Part B: dimension to bow | replaced by the mother ship's MMSI (bits 132 to 161) for an auxiliary craft |
| 141–149 | Part B: dimension to stern | |
| 150–155 | Part B: dimension to port | |
| 156–161 | Part B: dimension to starboard |
Paste a real sentence into the AIS message decoder to see these fields filled in.
All message types
| Type | Name |
|---|---|
| 1 | Position report, scheduled (Class A) |
| 2 | Position report, assigned schedule (Class A) |
| 3 | Position report, response to interrogation (Class A) |
| 4 | Base station report |
| 5 | Static and voyage related data (Class A) |
| 6 | Binary addressed message |
| 7 | Binary acknowledge |
| 8 | Binary broadcast message |
| 9 | 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 broadcast binary message |
| 18 | Standard Class B equipment position report |
| 19 | Extended Class B equipment position report |
| 20 | Data link management message |
| 21 | Aid-to-navigation report |
| 22 | Channel management |
| 23 | Group assignment command |
| 24 | Static data report (Class B) |
| 25 | Single slot binary message |
| 26 | Multiple slot binary message with communications state |
| 27 | Long-range AIS broadcast message |