Undesignated VHF DSC Distress Alert at 04:20
At 04:20 you are alone on the bridge of a 16 m workboat 7 nm off a rocky headland, making 8 knots in a 20-knot south-westerly, visibility 2 nm. Your 25 W VHF/DSC controller, with a correctly entered MMSI and a connected GPS, sounds the two-tone alarm and shows: distress, channel 70; MMSI 2320xxxxx; position 4.1 nm bearing 030°T from you; nature of distress undesignated; time 04:19. You listen on channel 16 for three minutes: nothing. Your DSC log shows no acknowledgment from any coast station, and AIS shows no target at the reported position. The nearest other vessel is a trawler 2 nm north; a ferry is 9 nm south. You are much the closest. The trawler calls you on channel 6: "Did you hear that?"
1. What do you transmit, on what channel, and when, in the first ten minutes?
Read the worked answer
Do not acknowledge at once. If every receiving ship acknowledges immediately, the DSC system is blocked and the coast station's own acknowledgment is buried. Instead:
- Note the alert details and plot the position; confirm your own GPS and MMSI are correct so your reply carries a valid position.
- Keep a continuous watch on channel 70 and channel 16; listen for the coast station.
- Under IMO guidance, if no coast station has acknowledged within about 5 minutes, acknowledge the alert yourself (by DSC or by radiotelephony on channel 16 addressed to the casualty) and inform the RCC or coast station by the fastest means available, state clearly that you are not the casualty, and give your position, course, speed and ETA.
- Turn toward the position at best speed, keep a radar and visual lookout, and stay on 16. Do not transmit a MAYDAY RELAY at this stage: relay is for when you are certain distress exists and nobody is handling it.
The alert is undesignated, so you have no idea what the emergency is - the 5-minute wait is a procedure, not a reason to do nothing.
2. How do you answer the trawler, and why should you not simply carry on the conversation on channel 6?
Read the worked answer
Answer briefly: "Yes, we heard it, we're going - switch to one-six and stand by." Tell it not to transmit on channel 70.
Channel 6 is an intership channel and it is perfectly good for coordinating with the trawler - later. It is the wrong place for the first response because distress, urgency and safety traffic belongs on channel 16, and the DSC alert on channel 70. If you and the trawler start a discussion on 6, you split the traffic: the coast station, the ferry and any responding aircraft are watching 16, not 6. An aircraft joining the search will call on 16.
Keep every transmission short - you may be one of several stations transmitting, and there may be a second casualty you cannot see in 2 nm visibility. Channel 6 becomes the right channel once the RCC or the on-scene coordinator assigns it.
3. At 05:05 you arrive and find a liferaft with three people, sea 1.5 m, helicopter 20 minutes out. The coast station asks you to act as on-scene coordinator. What is your communications plan and what do you report?
Read the worked answer
Accept only if you can actually do the job - on scene, with working communications, that is yes.
Report first, on channel 16, to the coast station/RCC: position; number of persons; apparent condition; wind, sea and visibility; other units present; your intentions (leeward approach, recovery); and the channel you will use.
Then split the channels:
- Channel 16 - the RCC and the helicopter. Keep the watch; answer promptly.
- Channel 6 - ship-to-ship with the trawler and any other unit. Tell the trawler to stand by as a lee and a spotter, not to close unless directed.
- Channel 70 - leave alone. No voice.
When the helicopter arrives, give it wind speed and direction, your course and speed, and the position of the raft relative to you, and clear the frequency when asked. Log every transmission with time: alert received, acknowledgment sent, arrival on scene, persons recovered. That log is what the investigation will read.