You can search for a vessel by looking up MMSI, IMO, name, or call sign.

Results will come back with exact or close matches to your search term. However, search results with incorrect information, duplicate vessels, or duplicate MMSIs and/or call signs can occur.

Using search filters can help to refine the results if you have additional information about the vessel.

AIS broadcasts can be categorised to two message types. Position (dynamic) messages contain information about a vessel’s location and motion, while static messages contain information about vessel and voyage details. The only identifier connecting messages together through time is the vessel’s MMSI, a nine-digit number which is assigned to an AIS unit upon registration.

All vessels with an AIS transponder(s) will have a MMSI. A MMSI is also used for handheld VHF transceivers with Digital Selected Calling (DSC) and Global Navigation Satellite System (GNSS). A MMSI is intended to be unique, but a vessel may have several MMSIs associated with it because Aids to Navigation (AtoN) often also have a MMSI assigned and this includes mobile AtoNs such as fishing buoys¹. Fishing buoys can also arbitrarily be assigned unregistered MMSIs.

A vessel’s MMSI can change and this is required if a vessel reflags. It can also occur when a vessel’s ownership is changed. A MMSI can also be reused when it is reassigned to another vessel². The MMSI is issued by a country’s telecommunication authority, ship registry or relevant licensing authority³. The MMSI is overseen by the International Telecommunication Union (ITU)¹.

The IMO ship identification number scheme is a way to enhance maritime safety and pollution prevention, and to facilitate the prevention of maritime fraud. The IMO ship identification number is intended to be unique. Not all vessels require a number, and the requirement depends on the size and type of vessel⁴.

The IMO ship identification number is intended to be a permanent number for each vessel. The number is never reassigned. There is a central manager for the scheme, S&P Global Market Intelligence (formerly IHS Maritime)⁴.

A call sign is required for radiocommunications. It is used when communicating over the ship’s radio and is generally associated with a vessel’s radio license. A vessel’s call sign is intended to be unique. An MMSI and call sign are often associated². However, an AIS transponder does not require a call sign, so not all vessels with an AIS transponder will have a call sign.

A vessel’s call sign can change, and this is required if a vessel reflags. It can also occur when a vessel's ownership is changed. A call sign can also be reused by reassigning it to another vessel. A call sign is issued by a country’s telecommunication authority, ship registry, or relevant licensing authority².

A vessel’s name is generally not required to be unique and a vessel name is not required for an AIS transponder.