Should a Ship Acknowledge a DSC Distress Alert?
At 2245 UTC, the 499 GT US-flag vessel MV Coral Trader is in Sea Area A2 in the Straits of Florida, 28 nm southwest of a DSC distress alert. The watch officer on 2187.5 kHz sees a distress alert from MMSI 367123456, nature "flooding", position 24°30.0′N 80°45.0′W. No coast station acknowledgment is heard on 2182 kHz or channel 16. The DSC controller displays soft keys labelled "ACK" and "RELAY"; the audible alarm is loud. The master is asleep, and the officer is tempted to press ACK to silence the alarm and confirm that help is coming. The vessel is not a dedicated SAR unit, but it has a SART, a rescue boat, and a crew trained in first aid. Channel 16 carries only routine chatter from sport fishermen.
1. Should the vessel transmit a DSC acknowledgment? Explain the rule and the risk.
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No. In the GMDSS, ship stations do not acknowledge DSC distress alerts by DSC. DSC acknowledgment is the responsibility of a coast station or RCC. A ship that presses ACK can mislead the distressed station into believing that a rescue authority has received the alert and that assistance is organized. It can also suppress further alerts or relays and create confusion when multiple ships acknowledge.
The correct action is to silence the alarm locally without transmitting, note the time, MMSI, position, and nature of distress, and listen on 2182 kHz and channel 16. If the vessel is in a position to assist, it should acknowledge by radiotelephony to the distressed vessel or coast station, not by DSC. The "RELAY" function is also not pressed reflexively; a distress relay is transmitted only when the alert is unacknowledged by a coast station and the ship is in a position to help. Pressing ACK to quiet the bridge is not a valid reason to transmit.
2. What should the officer do in the next five minutes, including whether to relay?
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The officer should silence the alarm, log the details, and keep a continuous listening watch on 2182 kHz and channel 16. If nothing is heard from a coast station, attempt a radiotelephony acknowledgment to the distressed vessel: 'MAYDAY, [distressed vessel name repeated three times], this is Coral Trader, received your DSC distress alert, acknowledge.' Give own position and state that the vessel is proceeding or standing by as appropriate.
If the distressed vessel does not answer and no coast station acknowledges within a short interval, the officer may transmit a MAYDAY RELAY on 2182 kHz and channel 16 to the coast station, identifying Coral Trader and passing the distressed vessel's MMSI, position, nature, and time of alert. A DSC distress relay may be used if the equipment supports it and the original alert remains unacknowledged, but voice relay to a coast station is clearer. The master should be called, and the vessel should prepare to assist without abandoning its own safe navigation.
3. If the distressed vessel later cancels the alert, what should Coral Trader do?
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If a voice or DSC cancellation is received, acknowledge it on the frequency in use, cease distress traffic, and resume the normal watch. The officer should log the cancellation, the time, and the source, and notify the master. If Coral Trader had transmitted a MAYDAY RELAY, it should inform the coast station that the original distress was cancelled so that SAR assets are not launched unnecessarily.
If the cancellation is a false-alert cancellation, the distressed vessel is responsible for cancelling on channel 16 and by DSC; other ships should not keep repeating the distress. If the situation is ambiguous, for example the vessel says the flooding is under control but the crew is still in danger, the coast station should decide whether to continue the response. Coral Trader should not unilaterally resume routine traffic until it is satisfied that no distress exists.