Glossary · Equipment & tracking
IMO number, MMSI and call sign: which one to trust
Also known as IMO number, MMSI, and Call sign.
Ships change name, flag and owner. Only one identifier survives that, which matters when you are confirming the vessel carrying your fruit.
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The IMO number is a permanent seven-digit number fixed to a ship’s hull for life; the MMSI and the call sign are radio identities that the flag state assigns and that change when the ship changes flag. Only the IMO number survives a sale, a new name and a new flag, which makes it the one to check when you confirm the vessel carrying your fruit.
| Identifier | Format | Assigned by | Changes when |
|---|---|---|---|
| IMO number | “IMO” and 7 digits | S&P Global, for the IMO | Never |
| MMSI | 9 digits | The flag state | The ship changes flag |
| Call sign | Letters and digits | The flag state | The ship changes flag |
| Vessel name | Free text | The owner | Sale, charter, rebranding |
Why the difference matters for your cargo
The MMSI is what AIS broadcasts, so it is what most tracking sites search by. Its first three digits identify the flag: 477 is Hong Kong, 636 and 637 are Liberia, 538 is the Marshall Islands. When a ship changes flag it takes a new MMSI, and the old one can later go to a different vessel. Data filed under an MMSI is not guaranteed to be about one ship.
The IMO number does not move. It is never reassigned, it is painted on the hull and printed on the ship’s certificates, and its last digit is a check digit, so a typing mistake usually fails instead of finding another ship.
The vessel name is the weakest of the four. Names are reused, and a search can return several ships at once. If a name is all you have, confirm it against the IMO number before you believe any position.
None of these follows your container. After a vessel substitution or a transshipment your box is on a different ship. The identifiers tell you which ship a carrier’s milestone refers to; the container or bill of lading number is what follows the cargo.
IMO number vs MMSI number goes further: how the check digit works, where to look each number up, and a thirty-second check of the ship named on your booking.
Trackberry keeps the containers you already have on the water in one place: tracking, documents and a live ETA. See how it works for produce importers, or book a 20-minute chat.
FAQ
What is the difference between an IMO number and an MMSI?
The IMO number is permanent and fixed to the hull, surviving sale, renaming and a change of flag. The MMSI is assigned by the flag state, changes when the ship changes flag, and can later be reassigned. AIS broadcasts the MMSI; the IMO number is what makes an identification last.
Does the IMO number change if the ship is sold or renamed?
No. It stays with the ship for its whole life and is never given to another vessel.