An MMSI (Marine Mobile Service Identity) identifies a marine radio station, typically a ship or shore station. This 9 digit number is globally unique. In marine communications, the MMSI is used in radios equipped with DSC Digital Selective Calling. A DSC-equipped VHF radio allows the operator to enter an MMSI and a chosen channel. The radio then issues a call which is received only by the selected station which generates an audible alarm. The operator of the receiving station can acknowledge the call, whereupon both sets switch to the selected channel for voice communication as normal. DSC relieves the station operator from keeping a listening watch on a calling channel, typically channel 16.
This is particularly useful when calling a ship identified by AIS. AIS transmitters are mandatory on vessels over 300 tons and passenger vessels and are increasing common on pleasure vessels. The transmitter transmits the ship's MMSI, its latitude and longitude, course, speed, turn rate and other data regularly on a VHF frequency. AIS receivers are now common on yachts, often interfaced to chart plotters. In the past a yacht wishing to alert a ship which appears to be coming too close could only call generally on channel 16 but would have difficulty identifying the specific ship amongst several within range. With AIS and DSC, the yacht can key in the MMSI and direct a VHF call to the specific ship.
The International Telecommunication Union maintains a database called MARS (Maritime mobile Access and Retrieval System) which includes MMSI numbers and data about the ship or facility to which the number is allocated. Data content is the responsibility of the national authorities which administer MMSIs. In the UK this authority is Ofcom. The MARS database is searchable online for the MMSI number, the yacht name or the callsign.
Some users have only email access to the web, for example cruising yachts with email via SSB provided by organisations such as Sailmail or the Ham radio network. To access MARS via email, send an email to cwsail@s2w.m.ac.nz with the subject line formated as follows:
If the search results in a match, the available data for ship are formated into an email which is returned to the originator. If there are multiple matches, the MMSI numbers and the country are returned.
MMSIs are allocated by Administration/Geographical areas which are coded using ITU-specific codes. These are mostly aligned to countries but there are some differences. For example Alaska (ALS) is distinct from the USA (USA). The full list of codes and Areas is here
A simpler interface using HTML is also provided. This may be suitable for use with a mobile phone.