Maritime Communications (GMDSS) and Signals
GMDSS questions test equipment knowledge and procedure under pressure: which frequency for which sea area, how to raise and cancel a distress alert, and how to relay when the casualty cannot transmit. Signals questions test the International Code of Signals and the Annex IV distress signals.
Sea areas and carriage
- A1 - VHF coverage of at least one coast station (DSC on Channel 70, radiotelephony on Channel 16).
- A2 - MF coverage (DSC 2187.5 kHz).
- A3 - Inmarsat coverage (approximately 70°N to 70°S).
- A4 - remaining polar waters, requiring HF (DSC on 4207.5, 6312, 8414.5, 12577 and 16804.5 kHz).
Equipment
406 MHz EPIRB with 121.5 MHz homing; 9 GHz SART; NAVTEX on 518 kHz for international English broadcasts; Inmarsat-C with SafetyNET; two-way VHF radiotelephones for survival craft. Distress, urgency and safety prefixes are MAYDAY, PAN PAN and SECURITE, each sent three times.
Distress relay and false alerts
On receiving a DSC distress alert, keep watch on the associated radiotelephony channel. If no coast station acknowledges within about five minutes, a ship may transmit a distress relay alert, then acknowledge by radiotelephony and inform the RCC. A false alert must be cancelled immediately by the same means used to transmit it, and by radio to the nearest coast station.
Worked example - reading a DSC distress alert
Alert received: MMSI 636019825, nature 108, position 29°12'N 032°40'E, time 0342 UTC.
- First digit 6 means a ship station; MID 636 is Liberia, so this is a Liberian-flagged vessel.
- Nature 108 is abandoning ship.
- The position is near the southern entrance of the Gulf of Suez. Action: acknowledge/relay if no coast station has done so, broadcast a MAYDAY RELAY, keep a continuous listening watch, plot the position, and inform the master and RCC - bearing in mind the Gulf's traffic density and limited diversion options.
Signals
International Code: flag N over C means "I am in distress and require immediate assistance". Single-letter meanings must be known, with 'A' meaning "I have a diver down, keep well clear at slow speed".
Traps that cost marks
- Transmitting a distress relay before waiting for the coast station's acknowledgement.
- Using Channel 16 for DSC instead of Channel 70.
- Saying the EPIRB transmits on 9 GHz (that is the SART).
- Forgetting to cancel a false alert on the equipment and with the coast station.