GMDSS and Marine Communications
What the exam tests
GMDSS questions test the SOLAS Chapter IV radio installation, sea areas, distress alerting and the correct operational use of DSC, EPIRB, SART and NAVTEX.
Core rules
- Sea area A1 has VHF coast radio coverage; A2 has MF; A3 has Inmarsat coverage; A4 is outside A1 to A3 and relies on HF.
- VHF DSC uses channel 70; distress, urgency and safety voice traffic follows on channel 16. MF DSC distress is on 2187.5 kHz.
- The 406 MHz EPIRB alerts the satellite system and provides homing; it must be registered to the ship.
- The SART operates in the 9 GHz band and is detected by ship or shore radar.
- NAVTEX broadcasts maritime safety information on 518 kHz in English.
- Batteries, radio log, daily tests and reserved distress frequencies are survey and operational items.
Worked example
A vessel in Sea Area A2 has an engine-room fire that cannot be controlled. The radio operator selects the DSC distress alert on MF, includes the ship identity and position, then transmits a Mayday on the associated voice frequency. The message states Mayday, ship name and call sign, position, nature of distress, assistance required and persons onboard. Reason: the DSC alert starts the distress process; the voice Mayday gives rescue coordinators the information needed. If a false alert is sent, it must be cancelled immediately by the correct procedure.
Traps
Using VHF channel 16 for DSC; failing to register the EPIRB; assuming one battery covers all equipment; not cancelling a false alert; omitting position and nature of distress from the Mayday.