How to Find a Vessel Using MMSI
Every AIS message a ship sends starts with the same thing: its MMSI. That makes the MMSI the fastest way to pick a single vessel out of the tens of thousands on a live map. This guide shows you how to find a vessel by MMSI, how to read what the number tells you, and when to use it instead of an IMO number.
What is an MMSI number?
MMSI stands for Maritime Mobile Service Identity. It is a nine-digit number that identifies a ship's radio station, used by AIS, digital selective calling (DSC) radios and satellite distress systems.
The flag state's telecommunications authority assigns the MMSI when the ship is registered, under rules set by the International Telecommunication Union (ITU). Unlike IMO numbers, MMSIs are not limited to large ships. Fishing boats, tugs, yachts and inland craft fitted with AIS or DSC radios also carry one.
How to read a vessel MMSI
The first three digits of a ship's MMSI are its Maritime Identification Digits (MID), which tell you the flag country. The remaining six digits identify the individual vessel.
| MID | Flag state |
|---|---|
| 232 | United Kingdom |
| 351 | Panama |
| 419 | India |
| 477 | Hong Kong, China |
| 538 | Marshall Islands |
| 563 | Singapore |
| 636 | Liberia |
Some countries have several MIDs. Numbers that do not start with an MID belong to other kinds of stations. For example, an MMSI starting with 00 is a coast station, 111 is a search-and-rescue aircraft, 970 is an AIS search-and-rescue transmitter (AIS-SART), and 99 is an aid to navigation such as a buoy or lighthouse.
Where to find a vessel's MMSI
- AIS data. The MMSI is in every AIS message, so it appears on all vessel tracking platforms.
- The ship's radio license, issued by the flag state.
- The VHF/DSC radio and AIS transponder on board, which display the number in their settings.
- Ship particulars and Q88 forms shared during chartering.
- The ITU's MARS database, which lists registered ship stations and their MMSIs.
How to find a vessel by MMSI: step by step
- Check the format. A ship's MMSI should be nine digits and start with a valid MID.
- Open an MMSI vessel search. Use an AIS tracking platform such as Navtrac.
- Enter the MMSI number. Type all nine digits, without spaces.
- Confirm the vessel. Compare the returned name, call sign, flag and ship type with your records.
- Track the vessel. Open its page to see its current position, speed, course, destination and recent track on the live map.
MMSI vs IMO number: which should you use?
Both numbers identify a ship, but they do different jobs.
| MMSI number | IMO number | |
|---|---|---|
| Digits | 9 | 7 |
| Identifies | The ship's radio station | The ship's hull |
| Issued by | Flag state, under ITU rules | S&P Global, on behalf of the IMO |
| Changes when reflagged | Yes | No, permanent for life |
| Carried by small craft | Often | Rarely |
| In every AIS message | Yes | Class A only |
Use an MMSI lookup when you want to track vessel by MMSI in real time, especially smaller vessels that have no IMO number. Use the IMO number when you need a permanent identity for history, compliance or sanctions checks.
Pitfalls to watch for
- Reflagged ships. A vessel MMSI changes when the ship changes flag, so an old number may now belong to nobody, or to a different ship.
- Duplicate or default numbers. Badly configured transponders sometimes broadcast an invalid MMSI such as 000000000 or 123456789, or two ships may share one by mistake.
- Typos. One wrong digit points to a completely different vessel, so always check the name and flag that come back.
Run an MMSI lookup with Navtrac
Navtrac decodes real-time AIS data, matches every message to its MMSI, and plots the vessel on an interactive map. Search by MMSI, confirm the ship, and follow its movements, port calls and maritime traffic around it in real time.
Find a vessel on Navtrac using its MMSI number.