AIS message type
AIS message type 27: Long-range AIS broadcast message
A compact position report meant to be heard by satellites. What type 27 carries, who sends it, how often, and how to read it.
What type 27 is
Type 27 packs MMSI, navigational status, position, speed and course into 96 bits, with coarser resolution: position to 1/10 minute, speed in whole knots, course in whole degrees. It is sent on a separate pair of long-range channels (AIS 3 and 4, 156.775 and 156.825 MHz), so a terrestrial receiver tuned to the two standard channels does not hear it.
How to read it
This site's positions come from shore-based receivers only, so type 27 is a good reminder of what we do not cover: it exists to reach satellite receivers. Where a type 27 does reach a feed, it is a low-resolution fix with a coarser position than a type 1.
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 | Position accuracy | |
| 40–43 | Navigational status | |
| 44–61 | Longitude | 1/10 minute; 181° = not available |
| 62–78 | Latitude | 1/10 minute; 91° = not available |
| 79–84 | Speed over ground | whole knots; 63 = not available |
| 85–93 | Course over ground | whole degrees; 511 = not available |
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 |