Global Maritime Distress and Safety System

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The Global Maritime Distress and Safety System (GMDSS) is a worldwide system for automated emergency signal communication for ships at sea developed by the United Nations' International Maritime Organization (IMO) as part of the SOLAS Convention.^[1]: 1

It is a set of safety procedures, types of equipment, and communication protocols used for safety and rescue operations of the distressed ships, boats, and aircraft. It is supplemental to the International Convention on Maritime Search and Rescue (ICMSaR) adopted in 1979 and provides basis for the communication.^{[1]: 1 [2]}

GMDSS consists of several systems which are intended to perform the following functions: alerting (including position determination of the ship in distress) ships in the vicinity and ashore authorities,^[1]: 1 search and rescue coordination, locating (homing), maritime safety information broadcasts, general communications, and bridge-to-bridge communications. Specific radio carriage requirements depend upon the ship's area of operation, rather than its tonnage. The system also provides redundant means of distress alerting, and emergency sources of power.

Recreational vessels do not need to comply with GMDSS radio carriage requirements, but will increasingly use the Digital Selective Calling (DSC) Marine VHF radios. Offshore vessels may elect to equip themselves further. Vessels under 300 gross tonnage (GT) are not subject to GMDSS requirements.^[1]: 1