AIS ship and cargo type · Special craft
AIS ship type 53: Port tender
Ship type 53 is “Port tender” — 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 53 means
A port tender — a small craft serving ships in harbour or at anchor with crew, stores or officials.
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 3 → in this range the units digit is not a cargo qualifier: 53 as a whole means “Port tender”.
- Therefore: Port tender.
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.