The Cold-Water Immersion Decision
A rescue swimmer is briefed on a man-overboard drill in water at 12 °C. A person in 12 °C water loses heat rapidly; survival time before severe incapacitation is roughly 30 minutes for an average adult, and useful movement of the limbs is lost well before that. The ship can turn and reach the casualty in 9 minutes if the drill is run at full speed, but the turn manoeuvre at full speed raises the risk of a secondary man-overboard from the deck party. At reduced speed the recovery takes 16 minutes but the secondary risk is much lower. The officer of the watch must choose a recovery profile and justify it against the cold-water timeline.
1. Compare the two recovery times against the 30-minute survival figure and state the safer choice.
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Full-speed recovery: 9 min - well inside the ~30 min incapacitation window, leaving ~21 min of margin. Reduced-speed recovery: 16 min - also inside the window, leaving ~14 min of margin. Both are survivable in principle, but the full-speed option preserves a much larger margin against error or delay. The safer recovery-time choice is full speed, but only if the secondary man-overboard risk is controlled; the decision must weigh both hazards, not time alone.
2. The deck party is inexperienced and the sea state is moderate. How should that change the judgement?
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With an inexperienced deck party and moderate sea, the probability of a secondary man-overboard at full speed is materially higher. A second casualty in 12 °C water would consume the same 30-minute budget and could overwhelm the recovery team. The correct judgement is to use reduced speed with extra deck supervision, accepting the 16-minute recovery because it still sits inside the survival window, and to mitigate the lost margin by pre-positioning a lifebuoy and a spotter. Time margin is traded for casualty-prevention margin.
3. Identify the single most important factor the officer should monitor during the recovery.
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The casualty's condition and time-in-water, not the ship's speed. Cold-water incapacitation means the person may stop responding or lose grip before 30 minutes, so the officer should track elapsed immersion time continuously and be ready to escalate (faster approach, helicopter, additional swimmers) if the casualty's responsiveness drops. Speed is a means; the casualty's remaining survival budget is the governing variable.