Consequences of Sleep Deprivation(1 of 3 on sleep)
Learning Objectives
1) Appreciate why sleep deprivation is so dangerous.
2) Disasters arise from a chain of small problems.
3) Hallucinations are powerful, even if the normal brain would know they are not correct.
4) Sleep Deprivation Offshore: Why Fatigue—Not Weather—Causes Many Sailing Disasters
Offshore sailors are conditioned to respect the obvious dangers: weather systems, equipment failures, and navigational hazards. We study weather models obsessively, inspect rigging for chafe, and carry redundancy for nearly every critical system aboard. We attend safety at sea courses that provide critical instruction about how to abandon ship, fire fighting and how to use flares. Yet one of the most powerful risk factors offshore often receives far less or generally no structured attention: sleep deprivation, its consequences and its risk mitigation.
As both a neuroscientist who studies sleep and a solo offshore sailor, I have come to believe that fatigue—not weather—is the most underestimated cause of serious offshore errors.
In this series of three blogs I will discuss the brain basis of sleep and how we can use this knowledge to our advantage while sailing offshore. I will give examples from studies of professional sailors as well as neuroscience-based examples. Importantly, when we are sailing offshore there are only rules of thumb. The unexpected happens – squalls, breakages, traffic. We have to have our brain rested to prepare for these eventualities. This is why napping (as you will see) is so important. I will finish the third blog entry by comparing solo and doublehanded sailing and how watch schedules can be tailored for the crew aboard.
Sleep is not a luxury. It is a biological requirement shared across nearly all species. During sleep, the brain undergoes profound changes in electrical activity and physiology. One recently discovered process is activation of the glymphatic system, a sleep‑dependent pathway that clears metabolic waste products from the brain. When we do not sleep, this system does not function effectively. Sleep is required for memory consolidation and is required for clarity of thought. Have you ever been driving a car late at night while tired and noticed how your reaction times are slowed and ability to follow simple routes can be impaired? This is the consequence of sleep deprivation.
Sleep deprivation degrades emotional regulation, memory consolidation, executive function, and perceptual accuracy. These are precisely the functions required for safe offshore decision‑making. Imagine its 0300 after three nights at sea. There is an alarm. One needs to clearly identify the source of the alarm, identify the risk and act to prevent a serious consequence, whether that be a collision, engine overheating or water ingress. Is your brain in a state to handle the information, troubleshoot and make decisions?
Fatigue has contributed to major disasters including the Challenger space shuttle accident, Chernobyl, Three Mile Island, and the Exxon Valdez oil spill. In each case, systems did not fail first, humans did. Disasters are not generally due to one action, but instead are due to a cascade of small errors. This is known as the Swiss cheese model of accidents. A disaster doesn’t usually happen due to one big mistake. Instead, multiple small failures line up, just like the consequence of aligned holes in Swiss cheese.
In the Challenger space shuttle disaster, the explosion of the solid rocket booster was ultimately due to the failure of an O-ring. But, this wasn’t the single problem. Other factors included the cold weather which led to the O-ring failure. But hours before take-off, mission control engineers had to make a go-no-go decision in the middle of the night under external pressure for the flight to proceed. The investigation into the disaster noted “.... certain managers involved in the launch had only slept two hours before arriving to work at 1 a.m. that morning.” The report went on to say “The willingness of NASA employees in general to work excessive hours, while admirable, raises serious questions when it jeopardizes job performance, particularly when critical management decisions are at stake."
Similarly at sea, sleep deprivation can and will impair our decision-making ability which can contribute to cascades of events leading to significant consequences on performance and potentially, to disastrous outcomes. There are numerous examples of highly experiences sailors who pushed too hard, slept too little and ended up with serious consequences as listed beneath.
But even before we get to extended sleep deprivation, even short periods of sleep deprivation cause simple consequences. Even after a few hours of extended wakefulmness reaction times are lengthened. Thinking can be confused. Decision making is impaired. 24-48 hours of sleep deprivation can cause hallucinations and sleepwalking. I have personally experienced vivid auditory and visual hallucinations offshore. In one example, I was beneath deck sailing solo and two crew mates spoke to me in a foreign language. I answered in their mother tongue despite not knowing word of their native language. And it felt real.
A young racer had been sailing for days without sleep, but he was ahead of the fleet in the Solitaire du Figaro, a grueling, singlehanded race off the coast of France. Sailing into the harbor to the cheers of the crowd, he stepped from his boat onto the wharf to accept their congratulations—then his safety harness jerked him back. There were no crowds, no wharf. He was standing on the gunwale of his boat surrounded by empty ocean.
In one of Rich Wilson’s two successful Vendee Globe campaigns he reported serious hallucinations resulting from sleep deprivation. In this hallucination Rich spent the better part of 18 hours trying to figure out how he was going to download an anchor to his boat via his modem. He says that the whole thought processes felt incredibly realistic. At the time he did not know this was a hallucination. But if this is not enough to alarm you, his other comment was what worried him most was that his high-speed satellite connection was not working and he would have to use his slower connection to download the anchor. He spent hours trying to determine how to achieve this download at a low baud-rate.
While even short periods of sleep deprivation can lead to hallucinations, longer periods cause one to fall to sleep, in extreme cases one may not be able to be woken by alarms. In the 2022 Golden Globe Race, after a period of 30h with no sleep Guy DeBoer inadvertently fell asleep only to be awoken as he ran aground. In a well-known case Alex Thomson, sailing the IMOCO 60 Hugo Boss, had a lead of 230nm over the second placed vessel, with only 65nm left to the finish line. He took a nap, and his wristwatch failed to wake him. Reports indicate that it mal-functioned . He was awoken by crashing on the rocks.
Though I am not doubting the failure of the alarm, this example raises another point of concern: with extensive sleep deprivation an alarm that normally wakes you now can fail to do so despite functioning correctly. Put another way, the threshold to be woken is greater after sleep deprivation. Claudio Stampii, an ocean racer and sleep expert performed controlled sleep studies and showed beautifully the inability to be awoken in this linked video. For the failure to wake start the video at 8min 25sec.
These examples should cause alarm, and I highlight them to get your attention. As a consequence, critics argue that solo sailing violates COLREGS because a sleeping sailor cannot maintain a lookout. The more relevant comparison is this: a severely sleep‑deprived sailor awake on deck may be less safe than a rested sailor sleeping briefly with alarms, AIS, and disciplined systems monitoring.
The real question is not whether solo sailors sleep. They must. The question is how to sleep safely. To understand how solo sailors should sleep we first need to understand how we normally sleep.
Next in this sleep series: How the brain sleeps – and why it matters offshore
Sailor Takeaway
Fatigue is a primary offshore risk factor.
A cascade of small problems, of which sleep deprivation is one, can culminate in a disaster.
Sleep deprivation degrades judgment before sailors notice.
Hallucinations are neurological warning signs.
Managing sleep is a safety system.
It is not WHETHER sleep deprivation causes a problem, it is WHEN.
