Sea Areas and Carriage Requirements
Definitions
Sea Area A1 is within radiotelephony coverage of at least one VHF coast station with continuous DSC alerting. A2 is beyond A1 but within MF coast-station coverage with continuous DSC alerting. A3 is beyond A1 and A2 but within the coverage of an Inmarsat geostationary satellite, excluding A4. A4 covers the remaining polar areas outside Inmarsat coverage. Memorise these definitions precisely; questions frequently test the boundaries and the phrase "continuous alerting".
Carriage logic
For A1, the baseline is VHF DSC, VHF radiotelephony, an EPIRB, a SART or AIS-SART, and a receiver for MSI (NAVTEX or EGC). Moving to A2 adds MF DSC and MF radiotelephony, or an approved alternative. A3 adds an Inmarsat ship earth station or HF, depending on the option chosen. A4 requires HF DSC and HF radiotelephony with NBDP where appropriate, because satellite coverage is absent. Traps include forgetting the MSI receiver, assuming an EPIRB alone satisfies all alerting, and missing that A4 is defined by the absence of Inmarsat coverage, not by latitude alone.
Power and duplication
Carriage requirements extend to reserve power (typically a battery able to supply the distress and safety functions for a specified period), duplication of certain equipment, and sources of energy. Questions may test that the reserve source must be independent of the main and emergency generators and capable of supplying the required load.
Worked example
A yacht certified for A2 carries VHF DSC, VHF RT, MF DSC, MF RT, EPIRB, SART and NAVTEX, with a reserve battery supplying the VHF and MF distress functions. If it plans a Southern Ocean passage into A4, the MF set is insufficient and HF DSC/RT plus NBDP capability becomes necessary.
Rule of thumb
List the five GMDSS functions, then check that each is covered for the highest sea area the vessel will enter.