The most important aspect of this is he was wearing a 5mil wetsuit. All of the rest of the things they mentioned are much smaller factors in him staying warm. The wetsuit also makes him slightly more buoyant. I kayak in the winter and have a dry suit, and a 5mil wetsuit when the water gets a bit warmer. In the winter my survival time would be minutes unprotected. The most dangerous time of year is May and June as unprotected kayakers come out in response to the warm air temperature. But the water is still very cold.
In that water he would have succumb to hypothermia in hours. I spent 2 hours wading in water with no protection in the same temperature that he was in. My body temp was 95 degrees, lower than his after 72.
It's one thing to sit neutrally bouyant in a Scuba suit, or in a flotation device, with nothing but shivering to keep warm. Asleep, you can get hypothermia in water that is nearly at body temperature.
However, endurance athletes (like this 2.5-day-swimmer apparently decided he was) can keep warm by exertion. Competitive swimmers will keep warm, and actually sweat a great deal, in a very cold pool throughout an hour or two of practice in nothing but a speedo.
The problem only comes when one discovers, like the protagonist of Jack London's "To Build A Fire", that you lack the endurance.
Did anybody read the article?? One of the most important factors was staying in the fetal position- he even lost consciousness at times and was saved by a floatation device that kept his head above water.
heat production by effort is large, probably way more efficient than shivering so your chances are probably better if you can reach a destination by swimming.
Hypothermia starts at relatively high temperature (naked, below 25°c if I remember well)
There are records of people dying after hours of being exposed to 14°c without proper clothing (actually in the Philippine, if memory serves me well)
Our body (without technology like clothing or homes) are really just adapted to live around the equator at constant 27°c :-)
The Ph. are just off the equator. I’ve been in the water in northern Australia and the water was 30c and on the verge of being too warm. Definitely not refreshing, felt like a salty bath tub.
Due to water being a way better conductor of heat than air you lose heat up to 75% faster than in air. Even 30°C warm water can therefore quickly lead to hypothermia if unprotected. Ever seen scuba instructors in warm countries? While their customers would often submerge in nothing but a swimsuit the instructors would often wear 6mm full body wetsuits due to longer exposure. And yet a lot of them are shivering in the evenings.
I've been shivering in the water at 27 degrees Celcius in Australia (diving, no wetsuit, sitting on the bottom). Admittedly I have a very slender build, but clearly 27 degrees is below my equilibrium temperature when not in activity.
There are a few adaptions to colder conditions like Brown Fat and shivering which directly converts calories into heat and work fairly well.
Body Size and insulating fat at can also make a huge difference. People in warmer climates are simply less adapted to cold conditions and therefore at greater risk for a given temperature.
PS: Some people can actually walk around without clothing or becoming cold in 40f weather and be perfectly comfortable. It's sleeping that's the greatest risk as you reduce metabolic activity while having a large surface area in contact with the ground.
There is wide variety in human resistance to cold, including cold water. It isn't surprising that someone who had lived in Russia could spend a great deal of time in the tropical ocean. Some people who live in the tropics can do that!
Incidentally, this variation seems not to be genetic, or maybe it is epigenetic. When visiting India during the "winter" with a friend who was born there but had lived in USA for decades, his family was shocked at how both of us were comfortable in short sleeves while they shivered in heavy coats.
