The GMDSS regulations (chapter IV of the International SOLAS Convention), require that every GMDSS equipped ship shall be capable of;
transmitting ship-to-shore Distress Alerts by at least two separate and independent means, each using a different radio communication service;
receiving shore-to-ship Distress Alerts; transmitting and receiving ship-to-ship Distress Alerts;
transmitting and receiving search and rescue co-ordinating communications;
transmitting and receiving on-scene communications;
transmitting and receiving locating signals;
receiving maritime safety information;
transmitting and receiving general radiocommunications relating to the management and operation of the vessel;
transmitting and receiving bridge-to-bridge communications.
The GMDSS applies to vessels subject to the SOLAS Convention - that is: Commercial vessels of 300 Gross Registered Tons (GRT) and above, engaged on international voyages.
The GMDSS became mandatory for such vessels
as at February 1, 1999.
Commercial vessels under 300 GRT, or those above 300 GRT engaged on domestic voyages only are subject to the requirements of their Flag State. Some Flag States have incorporated GMDSS requirements into their domestic marine radio legislation - however many have not.
Equipment vs Operational requirements
The major difference between the GMDSS and its predecessor systems is that the radio communications equipment to be fitted to a GMDSS ship is determined by the ship's area of operation, rather than by its size.
Because the various radio systems used in the GMDSS have different limitations with regards to range and services provided, the new system divides the world's oceans into 4 areas:
Area A1 lies within range of shore-based VHF coast stations (20 to 30 nautical miles);
Area A2 lies within range of shore based MF coast stations (excluding A1 areas) (approximately 100 - 150 nautical miles);
Area A3 lies within the coverage area of Inmarsat communications satellites (excluding A1 and A2 areas - approximately latitude 70 degrees north to latitude 70 degrees south); and
Area A4 comprises the remaining sea areas outside areas A1, A2 and A3 (the polar regions).
Australia and its surrounding SAR area are declared as Sea Area A3. There are no A1 or A2 areas in Australia.