A true "Holy Grail" for sailors, the Vendée Globe, this solo, non-stop round-the-world race, began on November 10, 2024. In the meantime, tAll participants will have to always keep an eye open on the course to follow, and on their boat subject to the hazards of the vast ocean. A constant attention which makes sleep a vital problematic question at the same time as a determining sporting stake.
To manage this issue, most skippers are accompanied by sleep specialists. Dr. Bertrand de La Giclais is one of them, he who has been dealing with sailors' sleep since the early 1990s. We interviewed him to better understand this problem of sleep at sea and how it is managed on a daily basis.
Sciences et Avenir: How is sailors’ sleep organized?
Dr. Bertrand de La Giclais: Sailors who embark on a solo race must prepare themselves for polyphasic sleep, a sleep fragmented into several phases of 10 to 40 minutes maximum. In fact, these are multiple naps that will number 3 to 6 per 24-hour period. The problem is to allow them to recover both physically and mentally with these relatively short periods of time compared to our sleep cycles on land.
That's to say ?
There are two types of restorative sleep: deep slow-wave sleep, which plays a physical regenerative role and is obtained in "normal" conditions after 40 minutes of falling asleep; and paradoxical sleep, which is a psychological regenerator and is generally achieved after 70 minutes of sleep. Sailors, despite the very short duration of their nap, must be able to achieve both types of sleep to keep going.
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Manage "intelligently" sleep debt
How do they achieve this restorative sleep with so little sleep?
After 48 hours at sea, they will accumulate what is called a sleep debt. It is by intelligently managing this debt that they can achieve deep slow-wave sleep or REM sleep. The idea is to be able to sleep little, but well. Because a sailor whose naps are not really restorative could encounter problems.
To better understand this phenomenon, we conducted a study with Kito de Pavant (a French browser, editor's note)) in order to draw up the time map for good sleep: the best rest slots. We know that between 11am and 12pm, a nap will not be of much interest in allowing the sailor to recover. This is also the case on land, where this slot is not conducive to real sleep. It is better to prefer the one from 1pm to 2pm, for example. Thus, the slots most conducive to restorative naps are distributed throughout this time map for good sleep.
But itThis time card may not correspond to the vagaries of navigation subject to the whims of rough seas. What happens in this case?
That's very true. That's why it is drawn up with margins of maneuver that allow the sailor to adapt it according to the conditions encountered during the race. In principle, I give the sailor 6 rest windows per 24-hour period. He must take at least 3 to avoid finding himself in the red.
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Sleep inertia and hypnagogic hallucinations: deadly risks
What is red?
These are the dangers inherent in lack of sleep that become deadly risks when you are alone at sea. The first risk is to be plunged into what is called sleep inertia: you are literally swallowed up by sleep that makes you let go. The sailors will then fall asleep for a normal cycle of 5 to 6 hours during which the boat is left to its own devices.
The second danger is psychological. These are hypnagogic hallucinations that result from a severe lack of paradoxical sleep. Sailors can have very strong and very disturbing hallucinations. Seeing a loved one on the boat. Seeing other boats around that do not exist. This can even go as far as the dromedary perched on the bow of the boat… These visions can literally make the sailor lose his head. Even more so when it is a solo race where no one is there to take care of him.
This interview was originally published on November 3, 2014.
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