MOB AIS

A Man Overboard AIS (MOB AIS) device is a small personal distress beacon, typically worn on a lifejacket or integrated into a personal flotation device, that activates automatically on water immersion or manually by the wearer. Once activated, it transmits AIS Class B-compatible position reports on AIS VHF channels 87B and 88B, enabling the vessel's own AIS display, ECDIS, or chart plotter to immediately plot the casualty's position and bearing. All MOB AIS devices are allocated MMSIs beginning with the prefix 972, as specified in ITU-R Recommendation M.1371, distinguishing them from vessel transponders (which use standard nine-digit MMSIs) and from AIS-SARTs (prefix 970) used on survival craft. This allows AIS equipment to present the target with a dedicated MOB symbol and alarm. The internal GNSS receiver provides position data within the transmitted message, reducing the time required for the vessel to return to the casualty. MOB AIS devices are not mandated by SOLAS as standard survival equipment but are increasingly adopted as best practice, particularly on vessels operating short-handed or in challenging conditions. Their effectiveness depends on the vessel maintaining a continuous AIS watch and having compatible display equipment. IMO Performance Standards for MOB devices are addressed in IMO Resolution MSC.246(83), which also covers AIS-SARTs. Battery life and transmission interval requirements are defined in that resolution and in ITU-R M.1371.