A biomathematical model for recreational sailing. How fatigue, circadian rhythm, and sleep debt affect cognitive performance on passage — and what you can do about it.
Three decades of research across chronobiology, sleep medicine, maritime safety, and biomathematical modelling — distilled into what matters for recreational sailors.
After 17 hours without sleep, cognitive performance drops to a level equivalent to the legal drink-drive limit in most countries. A normal first night watch on a two-crew passage.
Dawson & Reid (1997), Nature
Cognitive impairment at 3AM is roughly double that at 3PM for the same number of hours awake. The circadian rhythm creates a predictable danger window on every passage.
Folkard & Akerstedt, three-process model
Polysomnographic studies aboard ships show sleep efficiency drops to 78% in moderate conditions and as low as 30% in heavy seas. Your bunk is not your bed at home.
Bernd et al. (2023), polysomnographic study at sea
After 24 hours without sleep, impairment rises to approximately 0.10% BAC equivalent — well past the legal limit for driving in any jurisdiction.
Dawson & Reid (1997), independently replicated
The STCW mandates a maximum of 14 hours continuous wakefulness for professional mariners. A couple on a 120nm overnight passage will commonly exceed this before sighting their destination.
STCW Regulation VIII/1
Multi-day passages create compounding sleep debt that persists even when sailors feel adapted. The model tracks how impairment accumulates across days — not just hours.
Van Dongen et al. (2003), Sleep
Free PDF. Open access. No login required.
Click the button below to download your free copy. We've also sent it to your email.
Download PDF Also available at Preprints.orgResearch sources include
Nature · Sleep · Science Translational Medicine · Occupational and Environmental Medicine · Chronobiology International · Journal of Sleep Research · MAIB · US Coast Guard · EMSA