I don’t really see why the calculus should change depending on the rate of transfer of heat from you->environment … except that the stakes are higher when the rate of transfer is high. Moving your body leading to a drop in core body temperature is not a thing I’ve experienced in any environment - IME, you move, you get warmer all over.
The relevant question seems to be: would you expect the onset of hypothermia to be more of a danger than exhaustion due to overwork? I believe the answer is almost certainly yes, based on, f’rex this chart which shows hypothermia coming on in just a couple of hours in quite ordinary ocean temperatures (for comparison, the ocean temperature even in the hottest month of summer in my home city is right in that ‘medium hypothermia’ band, where it will get you in just a few hours - much less time than you’d expect the simple motion of moving your arms and legs to exhaust you)
Never mind my previous comment. Look at the amazing story of Guðlaugur Friðþórsson, who alone (from the crew of five of a capsized fishing boat) managed to swim for six hours to shore in freezing cold sea water, and then, barefooted, cross the lava fields of Vestmannaeyar to safety!
If there ever was a superman, that’s him…!
I just can’t work out the details. Maybe something simpler like a flotation device that resembles a piece of round colored candy with a hole in the middle.
No, you’ll actually be warmer, and it will help, although probably not for very long. Warmth doesn’t just move from your core to the extremities. Exercise generates heat. So when you kick your legs, your leg muscles generate heat.
Of course, moving your legs also increases the rate at which you lose heat to the surrounding water. And it increases blood flow, which tends to spread the heat in your body around. But net, you will heat up by swimming.
This is easy to demonstrate (and experience) experimentally. Compare getting in cold water and swimming vigorously to getting in cold water and just floating. You’ll be much colder in the second case. I’ve gone swimming in 60 degree water for a half hour. I was cold, but not exceptionally so. Setting in 60 degree water for a half hour would be awful.
That said, swimming vigorously is hard work. Most people don’t have the stamina to do it for very long at all, so this isn’t likely to increase your survival time in the water by much, unless you can swim to something that gets you the hell out of the water.
There is no known way to build an aid that allows people to float in the water for extended periods of time but engineers are working on it. So far, they have this prototype but is unknown if the basic idea can scale up. Maybe one day…
I think ‘several hours’ is overestimating human survival time by quite a bit. The oceans are pretty cold nearly everywhere on earth, and you are likely to succumb to hypothermia within an hour or two.
Not everywhere. You can get hypothermia for being in the ocean for an extended period of time in water less than 80 degrees but survival time isn’t limited by temperature alone much above that. Much of the Caribbean is about that warm or much warmer year round. Parts of the Gulf Coast of the U.S. get uncomfortably warm during the summer.
Here is a chart for Gulf Coast waters from Louisiana to Florida right now. They range from the mid to high 80’s to the low 90’s. You may die if you sink your boat but it isn’t going to be from hypothermia. Lots of tropical and subtropical regions of the world are the same.
I have swam (or more accurately, floated) for hours at a time without any aid while snorkeling and hypothermia was never an issue even during the winter. The salt water enables you to float well and you never get cold at all. I could stay out there if I had to until I passed out from lack of sleep but that is going to take a long time.
No. It depends entirely on the temperature of the water and the local climate. The survivors of the Indianapolis, for example, were immersed for three and a half days.