GMDSS General Principles and System Architecture
This domain tests whether you can place a ship in the correct sea area, state the GMDSS functional requirements, and select the minimum equipment that satisfies SOLAS chapter IV. Questions are usually scenario-based, so learn the boundaries, not just the labels.
Sea areas
- A1: within VHF DSC coverage of a coast station (Ch 70), typically about 20–30 nautical miles.
- A2: within MF DSC coverage (2187.5 kHz), outside A1.
- A3: within geostationary satellite coverage (about 70°N–70°S), outside A1/A2; HF may be used instead of satellite.
- A4: outside A1–A3, i.e. the polar regions.
Functional requirements (SOLAS IV/4)
Alerting (ship-to-shore), SAR coordination, locating, maritime safety information, general radiocommunications, and bridge-to-bridge communications.
Equipment logic
A1: VHF DSC, 406 MHz EPIRB, two SARTs (ships of 500 GT and above), NAVTEX or EGC receiver, two-way VHF for survival craft, and a reserve source of energy. A2 adds MF DSC (2187.5 kHz) with 2182 kHz radiotelephony. A3 adds Inmarsat-C (or HF DSC/NBDP). A4 requires MF/HF with DSC and NBDP. The 2024 SOLAS amendments also permit recognised mobile satellite services beyond Inmarsat and multi-system GNSS receivers.
Worked example
A 1,200 GT ship sails Mumbai–Colombo through A1, A2 and A3. Minimum fit: VHF DSC, MF/HF DSC for A2, Inmarsat-C for A3, EPIRB, two SARTs, NAVTEX, survival-craft VHF and battery. Reasoning: Inmarsat does not satisfy A2, and MF alone does not satisfy A3 unless HF is installed.
Traps that cost marks
- Treating A3 as "anywhere by satellite" - polar waters are A4.
- Naming Ch 16 as the GMDSS alerting channel; alerting is Ch 70 DSC.
- Reversing EPIRB (alerting) and SART (locating) roles.
- Forgetting that the NAVTEX/EGC receiver and reserve battery are carriage requirements.