Module 6 - Distress & Mayday
Mayday Threshold
What you will learn
Use a short release decision under pressure: current danger, remaining margin, assistance required and the consequence of delay.
A useful Mayday decision is not a list of named incidents. It is a release gate that prevents optimism, embarrassment or incomplete information from delaying a distress call.
Build the decision around four questions: Is a vessel or person in grave danger? Is the danger imminent rather than merely possible? Is immediate outside assistance required? Would delaying the alert materially reduce the chance of a safe response? The MCA threshold supplies the first three; the fourth is a practical check against waiting until the last possible moment.
Some incidents change category. A controllable engine failure in safe water may be routine or urgency. The same failure with a lee shore close aboard and no remaining means of arrest can become distress. A medical incident may begin as PAN-PAN for advice and become Mayday if the person's condition becomes immediately life-threatening and urgent rescue is required.
Do not downgrade because the crew has also activated a beacon, made a phone call or attracted a nearby vessel. Parallel alerting may help, but the Mayday voice message broadcasts locally, establishes distress traffic and provides details. Conversely, a Mayday does not relieve the skipper of collision avoidance, damage control, lifejacket, abandonment or recovery decisions.
Worked example
A fictional disabled yacht is 0.6 NM from danger and being set towards it at 1.2 kn with no effective means of arrest.
- 1Nominal time to danger is distance ÷ speed: 0.6 NM ÷ 1.2 kn = 0.5 hours.
- 20.5 hours is 30 minutes if the rate and direction remain unchanged.
- 3That number is an urgency warning, not safe waiting time: sea state, drift, failed attempts and rescue response all consume the margin.
Sense check: The calculation helps expose a shrinking margin; it does not promise thirty safe minutes or replace the Mayday threshold judgement.
Use a four-question release gate
Smoke is increasing below. The source has not been isolated, one escape route is becoming unusable and the crew needs immediate external assistance while preparing to abandon.
1. Danger
Uncontrolled smoke and loss of an escape route create grave danger to the vessel and people.
2. Time
The worsening conditions make the danger imminent; waiting for a complete fault diagnosis would consume rescue time.
3. Assistance
Immediate outside assistance is required, so release the Mayday while the crew continues emergency actions.
Sense check: If the explanation for waiting is 'we want to be completely sure first', test whether that delay is consuming the response margin.
Common mistake or limitation
- Using incident names as automatic priorities without considering severity, time and assistance needed.
- Treating a beacon or phone call as a reason to omit the local VHF distress procedure.
- Using the nominal time-to-danger result as permission to wait until the last minute.
Recap
- Test danger, imminence, assistance and the cost of delay.
- Reassess priority whenever the situation changes.
- A calculated margin is an alarm for action, not a guarantee of safe waiting time.
Optional quick check
Section 4 of 10
What is the safest interpretation of a calculated thirty-minute nominal time to danger?
Sources and factual review
Reviewed 1 September 2026 - Compass Revision editorial review.
Continue studying Distress & Mayday
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