What is GMDSS?

The SOLAS (Safety Of Life At Sea) International convention lays down a wide range of measures designed to improve and maintain the safety of shipping. It applies to a wide range of commercial and passenger vessels.

The GMDSS (Global Maritime Distress and Safety System) is an integral part of SOLAS and is a radio-based communications system designed to support the implementation of Search and Rescue (SAR) plans. The GMDSS provides for automatic distress alerting and locating in cases where a radio operator doesn't have time to send an SOS or MAYDAY call, and, for the first time, requires ships to receive broadcasts of maritime safety information which could prevent a distress from happening in the first place.

The GMDSS consists of several systems, some of which are new, but many of which have been in operation for many years. The system will be able to reliably perform the following functions: alerting (including position determination of the unit in distress); search and rescue co-ordination; 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 backup means of distress alerting, and emergency sources of power.

What is Digital Selective Calling?

Digital Selective Calling (DSC) uses digital data, rather than voice, to transfer information between radios. Using this mechanism provides several important benefits including increased volume and accuracy of data and the ability to direct the information to specific addressees (Selective Call). Communications range when sending digital signals is also improved.
DSC is primarily intended to initiate ship-to-ship, ship-to-shore, and shore-to-ship radiotelephone and MF/HF radio-telex calls. DSC calls can also be made to individual ships or groups of ships. DSC distress alerts, which consist of a preformatted distress message, are used to initiate emergency communications with ships and rescue co-ordination centres.

When fully implemented, DSC will eliminate the need for persons on a ship's bridge or on shore to continuously guard radio receivers on voice radio channels, including VHF channel 16 (156.8 MHz) and 2182 kHz. The 2182kHz listening watch aboard GMDSS-equipped SOLAS ships ended on 1 February 1999. The VHF channel 16 watch is currently scheduled to end on 1 February 2005.

What is a MMSI?

Maritime Mobile Service Identities (MMSI’s) are a series of nine digits, which are used to uniquely identify a radio station or group of radio stations. When sending a DSC message the MMSI is automatically included, and you can address messages to specific vessels or groups using their MMSI.

There are four different kinds of MMSI: Ship station identities; Group ship station identities; Coast station identities; Group coast station identities.

The MMSI has a standard format (just like a telephone number) and it identifies the type of station, country of registration and vessel identity. This information is stored in a database available to RCC’s 24 hours a day, for interrogation in an emergency.