Module 8 - Digital Selective Calling
Distress Alert Reception And Acknowledgement
What you will learn
Respond to a received VHF DSC distress alert without interfering with coast-station coordination or abandoning a casualty that still needs help.
A received alarm begins a listening and decision sequence. Stop interference, listen on Channel 16 and allow the normal coast-station acknowledgement window before a capable vessel responds by voice.
When a VHF DSC distress alert sounds, immediately cease any transmission that may interfere with distress traffic and continue a listening watch on Channel 16. Read the received message without delaying the watch: note the distressed identity, category, position and UTC shown by the set, then listen for the voice Mayday and coast-station coordination.
The MCA small-craft procedure says that if there is no DSC acknowledgement after five minutes, a vessel able to offer assistance may acknowledge by voice on Channel 16. Do not send an impulsive digital distress acknowledgement from a small-craft set or crowd the first moments with repeated calls while a coast station may be responding.
A useful voice acknowledgement identifies the casualty, identifies your vessel and states what assistance you can give, including ETA if proceeding. If the distress has not reached an appropriate coast station, use any available means to relay it. Safety of your own vessel and crew still governs what assistance is possible.
Worked example
A DSC distress alert shows yacht North Star at a position eight miles away. No coast-station acknowledgement or voice response is heard during the five-minute listening period. Your vessel can safely assist and has the details written down.
- 1Stop unrelated transmission, set Channel 16 and record the displayed identity, position and UTC.
- 2Listen for the Mayday, coast-station acknowledgement and other coordination for five minutes.
- 3If still unacknowledged, call by voice: identify North Star and its call sign or MMSI; identify your vessel; say RECEIVED MAYDAY; state the assistance and ETA you can safely provide; end OVER.
- 4Use another available route to alert an appropriate coast station and continue listening for instructions.
Sense check: The five-minute wait is not permission to ignore the casualty. It protects the initial coordination window while the receiving vessel prepares a useful response if none arrives.
Listen, record, then add useful capability
Several alarms and voices overlap after a received distress alert.
1. Protect the channel
Stop unrelated traffic and maintain the Channel 16 watch.
2. Build a record
Write identity, position, time, nature and any acknowledged instructions rather than relying on memory.
3. Respond proportionately
After the published interval, add a voice acknowledgement only when you can provide relevant assistance and no DSC acknowledgement has been heard.
Sense check: A response that gives no capability or blocks a coast station may make the channel busier without making the casualty safer.
Common mistake or limitation
- Acknowledging digitally immediately from any receiving small craft.
- Turning off the alarm and missing the Channel 16 voice message.
- Promising assistance without considering distance, conditions and own-vessel safety.
Recap
- Cease interference and listen on Channel 16.
- Allow five minutes for DSC acknowledgement before a capable vessel acknowledges by voice.
- State useful assistance and relay to a coast station when needed.
Optional quick check
Section 5 of 9
A DSC distress alert is received but no acknowledgement has yet been heard. What should a small craft do first?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
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