More about sea areas and related GMDSS equipment
Specific equipment requirements for ships vary according to the sea area (or areas) in which the ship operates. The GMDSS combines various subsystems - which all have different limitations with respect to coverage - into one overall system, and the oceans are divided into four sea areas:
- Area A1 Within range of VHF coast stations with continuous DSC alerting available (about 20-30 miles)
- Area A2 Beyond area Al, but within range of MF coastal stations with continuous DSC alerting available (about l00 miles)
- Area A3 Beyond the first two areas, but within coverage of geostationary maritime communication satellites (in practice this means Inmarsat). This covers the area between roughly 70 deg N and 70 deg S.
- Area A4 The remaining sea areas. The most important of these is the sea around the North Pole (the area around the South Pole is mostly land). Geostationary satellites, which are positioned above the equator, cannot reach this far.
Coastal vessels, for example, only have to carry minimal equipment if they do not operate beyond the range of shore-based VHF radio stations, but they may carry satellite equipment. However, some coasts do not have shore-based facilities, so although the ship is close to shore, the area counts as Area A2 or A3. Ships which do go beyond Sea Area A1 have to carry MF equipment as well as VHF - or Inmarsat satellite equipment. Ships which operate beyond MF range have to carry Inmarsat satellite equipment in addition to VHF and MF. Ships which operate in area A4 have to carry HF, MF and VHF equipment.