The Odd Case of the Group MMSI

There are three (four) very common numbers for sailboats. The first is the hull identification number assigned by the builder. The second is the documentation number assigned by a government or by a locality (i.e. in the US by a State.) The third is a individual “Maritime Mobile Service Identity” (MMSI) assigned by the government telecommunications bureau (i.e. The Federal Communications Commission in the U.S.) [The fourth number is the International Maritime Organization (IMO) number. it is assigned to big ships] An individual MMSI identifies a ship’s radio installation. In a sense it is the “digital” embodiment of the ship station call sign (e.g. Reboot’s radio call WDB8435 identifies the same equipment as the MMSI 336 958 630.) Since automatic information systems (AIS) transmitters are radios it is also used to identify an AIS transmitter. In a digital selective calling enabled radio one can “ring” another ship or shore station by using the DSC function and the called station’s MMS