GMDSS and Maritime Communications
The GMDSS system
You must understand the sea areas A1 to A4 and the equipment required in each. Know the functions of DSC, NAVTEX, EPIRB, SART and the portable VHF radios. Understand the distress, urgency and safety priorities and the correct procedures for a distress alert. Know the purpose of the continuous watch on VHF channel 16 and the DSC distress frequency. Understand the difference between a Mayday, a Pan-Pan and a Securite call.
Traps
A common trap is confusing the EPIRB, which transmits to satellites, with the SART, which responds to radar. Another is assuming NAVTEX covers all sea areas; it has limited range and is not available everywhere. Watch for questions on the correct silence periods and on the requirement to cancel a false alert immediately. Also be careful with the meaning of 'acknowledged' in DSC distress procedures.
Worked rule of thumb
For distress, use the sequence: Mayday, this is, vessel name and call sign repeated three times, position, nature of distress, assistance required, and any other information. For a false alert, transmit a cancellation on the same frequency immediately and inform the coast station. Remember the priority order: distress, urgency, safety, routine. If you hear a distress alert, do not transmit on the distress frequency unless you can assist or are acknowledging; keep a listening watch and log all communications.