The GMDSS is an internationally recognized distress and radio communication safety system for ships replacing the previous ship to ship safety system, which relied on a manual Morse code system on 500 kHz and voice radiotelephony on Channel 16 and 2182 kHz. The GMDSS is an automated ship to shore system using satellites and digital selective calling technology. The GMDSS is mandated for ships internationally by the International Maritime Organization (IMO) Safety of Life at Sea Convention (SOLAS), 1974, as amended in 1988, and carries the force of an international treaty. The procedures governing use are contained in the International Telecommunication Union recommendations and in the International Radio Regulations, and also carry the force of an International Treaty.
The main purpose of GMDSS is to prevent unanswered distress calls and delay in Search and Rescue actions when distress situations occur. GMDSS assures “... that any emergency at sea will result in a distress call and the response to that call will be immediate and effective” (IMO, Shipping Emergencies - Search and Rescue and the GMDSS, March 1999).
The GMDSS therefore provides that every ship, while at sea, shall be able to perform the following nine basic communication functions:
1. transmitting ship-to-shore distress alerts (by at least two separate and independent methods);
2. receiving shore-to-ship distress alerts;
3. transmitting and receiving ship-to-ship distress alerts;
4. transmitting and receiving search and rescue co-ordinating communications;
5. transmitting and receiving on-scene communications;
6.transmitting and receiving signals for locating;
7. transmitting and receiving maritime safety information;
8. transmitting and receiving general communications; and
9. transmitting and receiving bridge-to-bridge communications.
The SOLAS Convention provides that “… every ship shall be provided with radio installations capable of complying with the functional requirements … throughout the intended voyage …”. Thus every ship has to carry a core installation of basic equipment that is applicable to all waters, supplemented by additional equipment that extends the ships communications capabilities according to the specific waters in which she will sail. These supplementary requirements are defined by the distance offshore the ship will travel:
Sea Area A1: the area within the radiotelephone coverage of at least one VHF coast station in which continuous DSC (Digital Selective Calling) alerting is available;
Sea Area A2: the area, excluding Sea Area A1, within the radiotelephone coverage of at least one MF coast station in which continuous DSC (Digital Selective Calling) alerting is available;
Sea Area A3: the area, excluding Sea Areas A1 and A2, within the coverage of an Inmarsat geostationary satellite in which continuous alerting is available; and
Sea Area A4: an area outside sea areas A1, A2 and A3.
