AIS ship and cargo type · Special activities
AIS ship type 31: Towing
Ship type 31 is “Towing” — one of the 30s 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 31 means
A vessel engaged in towing. Tugs used for towing at sea commonly report 31, while harbour tugs often report 52 (tug). The two codes overlap in practice and the choice is the operator’s.
The 30s break the family-plus-qualifier pattern. Each code is its own meaning and describes what the vessel does — fishing, towing, dredging, diving, military operations, sailing, pleasure — rather than a hull family with a cargo declaration.
Reading the two digits
- Tens digit 3 → the special activities family, codes 30–39.
- Units digit 1 → in this range the units digit is not a cargo qualifier: 31 as a whole means “Towing”.
- Therefore: Towing.
Every code in the 30–39 range
| Code | Meaning |
|---|---|
| 30 | Fishing |
| 31 | Towing |
| 32 | Towing, length of the tow exceeds 200 m or breadth exceeds 25 m |
| 33 | Dredging or underwater operations |
| 34 | Diving operations |
| 35 | Military operations |
| 36 | Sailing |
| 37 | Pleasure craft |
| 38 | Reserved for future use |
| 39 | Reserved for future use |
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.