Distress, Urgency and Safety Communications (DSC and Voice)
Priority and formats
The exam tests whether you can choose the correct priority and pass the right information in the right order. Distress means grave and imminent danger and requires immediate assistance. Urgency means a serious situation that may become distress. Safety means an important navigation or meteorological message.
DSC distress alert
A VHF DSC distress alert is sent on Ch 70, MF on 2187.5 kHz and HF on 4207.5, 6312, 8414.5, 12577 or 16804.5 kHz. The alert carries the ship's MMSI, position, time and nature of distress. If the nature is unknown, use undesignated. After the alert, follow up on the associated voice or NBDP frequency unless the coast station directs otherwise.
Voice distress
Use MAYDAY three times, this is, ship name and callsign/MMSI, MAYDAY, position, nature of distress, assistance required, persons on board, and any other useful information. For urgency use PAN PAN three times; for safety use SECURITE three times. A distress relay uses MAYDAY RELAY. Distress traffic has absolute priority; other stations must keep silence unless they can assist.
Worked example: fire in the engine room. Send a DSC distress alert on Ch 70 with nature fire and position, then transmit MAYDAY on Ch 16 with the detail. If no acknowledgement arrives, repeat the alert or use another available system. The reasoning: DSC gets attention and position automatically, while voice conveys the detail and intentions.
Traps
Never send a voice MAYDAY on Ch 70. Do not use a distress alert for a simple breakdown without grave and imminent danger; that is a false alert. PAN PAN is not a lower-grade MAYDAY for a life-threatening medical emergency. If you trigger a false alert, cancel it by DSC or voice and inform the coast guard.