heat loss

[SDE Dennis]

I was snorkleing with my children in RI and as expected they would get cold after a short time. They have wet suits and I was wondering how much a hood would help.

I know that most heat is lost from your head above water. I was wondering if anyone knows how that translates underwater.

 

[LeadTurn_SD]

Since water conducts heat more efficiently than air, you can multiply the heat loss from the head that you'd experience on land by a factor of (??).... well, a lot

Hoods make a big difference. I wear a 3mm hood in the summer here in Hawaii, and a 5mm hood in the winter (where I dive in Hilo it is cooler than much of Hawaii due to fresh water runoff, the temps are often low 70's, on a VERY cold day in winter last year, 69 degrees).

Best wishes.

 

[SDE Dennis]

Since water conducts heat more efficiently than air, you can multiply the heat loss from the head that you'd experience on land by a factor of (??).... well, a lot

Hoods make a big difference.

Best wishes.

Yes hoods do make a big difference but I almost think that is to easy. Maybe heat loss from your head on land is so much because you are standing upright? Just thinking outloud.

 

[RJP]

Note, it's not that "most heat is lost from your head" but rather that your head loses disproportionately more heat per cm² than other parts of your body. IE your head may make up only 12% of your body's surface area but may account for 25% of your body's heat loss. (made up numbers for illustration.)

This is further compounded by the fact that your head cannot be completely covered like the rest of your body can be.

Lastly, to preserve warmth your body will shunt blood away from extremities towards vital organs... one of which is the brain. So while your body can keep blood out of your hands and feet, it doesn't have the luxury of keeping it from flowing to your head. (Behavior of some folks notwithstanding.)

 

[DTm]

Note, it's not that "most heat is lost from your head" but rather that your head loses disproportionately more heat per cm² than other parts of your body. IE your head may make up only 12% of your body's surface area but may account for 25% of your body's heat loss. (made up numbers for illustration.)

Thank RJP I know I had read something to that effect but could not remember it.

While, I agree that to the physiology is blood moved from the extremities like your hands, adding gloves has made a huge difference in my comfort in cold water.

 

[knowone]

No hood makes me feel like an African woman in Africa having been shopping for a block of ice.
Notwithstanding, when standing, a head is warmer because it is closer to the sun.

 

[SDE Dennis]

Thanks for the info.

 

[EGad]

Another factor to consider when thinking about why the head transfers heat quickly is the amount of blood vessels in the head. If you've ever gotten a facial or scalp laceration you'll know it bleeds like crazy. So that transfers heat very efficiently, much like a car's radiator. According to my water survival school's instructors and some quick googling of coast guard websites and the like, you lose body heat 25x quicker in water than air.

So there's the physics of it. But on a more practical note, I grew up snorkeling in RI. A hood helps a lot.

HTH,
Eric