Coastal Skipper and Yachtmaster Quiz · Safety and communications
GMDSS divides the sea into areas A1 to A4. What defines sea area A1, the band nearest the coast station?
A chart of GMDSS sea areas, not to scale. A coast station with an aerial stands on the coast on the left. Three bands spread out to seaward from it: the nearest, highlighted in gold, is labelled A1, the next A2 and the furthest A3.
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Within VHF range of a coast station that keeps continuous DSC watch, typically 20 to 30 miles off. Sea area A1 is within range of at least one VHF coast station with continuous DSC alerting, often 20 to 30 miles from the coast, depending on aerial heights. A2 is within MF DSC range of a coast station. A3 is the area beyond that covered by a recognised mobile satellite service the vessel is fitted for, and A4 is whatever remains. For vessels that GMDSS applies to, the sea area decides the radio equipment required; it is a sound guide for yachts too.
