Cold-Water Immersion Timelines for Fishing Crews: A Heat-Loss Bound and the Protection Budget of Low-Cost Immersion Layers

Fishing crews who fall overboard usually lose the ability to help themselves long before deep hypothermia develops, and full immersion suits are unaffordable for many small-boat crews. This paper computes, from a stated two-compartment (core and peripheral) heat-loss model, the time to incapacitation for an immersed wearer in water at 0-20 C in four clothing states: ordinary work clothes, work clothes plus a flotation layer (0.090 m2K/W, USD 85), a 3 mm neoprene layer (0.180 m2K/W, USD 180), and a full immersion suit baseline (0.450 m2K/W, USD 650). For an 80 kg wearer floating still in calm water at 10 C, computed times are 24.7 min (work clothes), 36.8 min (flotation layer), 80.8 min (neoprene), and 175.6 min (immersion suit). The neoprene step buys the most additional time per extra dollar, the flotation layer is the cheapest step and the only low-cost step addressing cold-shock drowning, and no insulation in the set removes the cold-shock window. Screening-level model; all results SIMULATED, NOT MEASURED.