AIS ship and cargo type · Special craft
AIS ship type 51: Search and rescue vessel
Ship type 51 is “Search and rescue vessel” — one of the 50s codes where each number is its own meaning. What it tells you, and how many vessels we can hear sending it right now.
What code 51 means
A vessel assigned to search and rescue, such as a lifeboat-service or coastguard rescue boat. Seeing one under way is not by itself evidence of an incident — SAR crews train and transit routinely.
The 50s also break the pattern. Each code names a role — pilot boat, search and rescue, tug, port tender, pollution response, law enforcement, medical transport — and the units digit is part of that name, not a cargo qualifier.
Reading the two digits
- Tens digit 5 → the special craft family, codes 50–59.
- Units digit 1 → in this range the units digit is not a cargo qualifier: 51 as a whole means “Search and rescue vessel”.
- Therefore: Search and rescue vessel.
Every code in the 50–59 range
| Code | Meaning |
|---|---|
| 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 (RR Resolution No. 18) |
What the code is not
The ship-and-cargo type is typed into the transponder by whoever installs or operates it. No authority checks it against the ship’s certificates, and it is broadcast in the static report every six minutes whether or not it is right. It describes what the operator says the vessel is, not what it is doing — that is the job of the navigational status.
For the whole decade structure in one read, see AIS ship type codes explained.