GMDSS regulations define three methods of ensuring availability of GMDSS equipment at sea:
- At sea electronic maintenance, requiring the carriage of a qualified radio/electronic officer (holding a GMDSS First- or Second-class Radio-Electronics Certificate) and adequate spares and manuals;
- Duplication of certain equipment; or
- Shore based maintenance
Ships engaged on voyages in sea areas A1 and A2 are required to use at least one of the three maintenance methods outlined above, or a combination as may be approved by their administration. Ships engaged on voyages in sea areas A3 and A4 are required to use at least two of the methods outlined above. The lower requirement for A1 and A2 areas recognises that being closer to shore, ships will have more opportunity to rectify problems.
The vast majority of ships do not opt for at sea maintenance preferring instead to duplicate the equipment and use shore-based maintenance (for A3 ships), or use shore based maintenance only (A1 and A2 ships).
GMDSS equipment is required to be powered from three sources of supply:
- ship’s normal alternators/generators;
- ship’s emergency alternator/generator (if fitted); and
- a dedicated radio battery supply. (The batteries are required to have a capacity to power the equipment for 1 hour on ships with an emergency generator, and 6 hours on ships not fitted with an emergency generator).