Global Maritime Distress and Safety System

The Global Maritime Distress and Safety System replaced the old reliance on manual radio watchkeeping and Morse code with an automated, satellite-and-terrestrial system that ensures a ship in distress can raise the alarm and that nearby vessels and rescue authorities will receive it. Made mandatory for most cargo and passenger ships under SOLAS, the GMDSS is built on the principle that alerting should not depend on a person happening to be listening at the right moment: equipment sends and receives distress messages automatically, and the burden of continuous listening watch is carried by the system itself.

The equipment a ship must carry depends on where it trades, defined by four sea areas. Area A1 is within range of shore VHF stations, A2 within MF range, A3 within the coverage of geostationary satellites, and A4 the polar regions beyond that satellite coverage. Ships fit a mix of equipment scaled to their area: digital selective calling on VHF, MF and HF for automated alerting; satellite communications for voice, data and distress; an emergency position-indicating radio beacon; search-and-rescue transponders; NAVTEX and satellite receivers for maritime safety information such as navigational and weather warnings; and portable VHF radios for survival craft.

The system organises the whole chain of alerting and response. A distress alert identifies the ship and its position and reaches coast stations and rescue coordination centres as well as ships in the vicinity, which are obliged to assist. Beyond distress, the GMDSS delivers the routine safety information mariners rely on, from gale warnings to notices to mariners. Officers must hold the appropriate GMDSS radio operator certificate, and the equipment is tested regularly, because in an emergency the reliability of the distress and safety communications can be the difference between rescue and loss.