Wetsuit ideal fit?

[JustinW]

Repeating ScubaDoo, you don't want it so tight around the neck that you pass out, thats not very good underwater. I have noticed that newbies frequently complain about the feeling of a 7mm or the tightness around the front of the neck when not used to a wetsuit. You won't believe how much water can slosh through a suit that on land appears to be very tight.
I find that a bit of baby shampoo watered down makes a wetsuit go on easy. If you are using this solution be mindful of where you are diving and that you aren't polluting everything with soap.

 

[spectrum]

A hood that is too tight can restrict blood flow in the neck area..(carotid arteries), and can also impair your ability to equalize.

Not to mention you might black out!

The thin layer of water between your skin and the wetsuit is what insulates and keeps you warm

That is not correct. Water is not an insulator, in fact it's a darned good conductor. If you could be dry in your wetsuit you would be warmenr... but then it owuld be a drysuit. The only thing you can sya thermally about water in a wetsuit is that you body warms it (using your personal energy) and then the suit keeps that water and yourself warm. Youf body tolerates this layer of wetness.

Pete

 

[spectrum]

In terms of controlling the neck openeing a 3 mil hooded vest worn under a full suit can be much more efective and easier to don than a bibbed hood.

Pete

 

[ScubyDoo]

Water is not an insulator, in fact it's a darned good conductor.

Its both an insulator AND conductor. Any level or space that separates your skin from the cold water or cold air is an insulator, regardless how thin. Its no different than the wall of a building, where even the paper thin building wrap is factored into the walls "u" or "r" value. Lets assume for arguements sake that the layer of water between your wetsuit and skin is say......6" thick, and is heated to body temperature. Or lets take it one step further...Lets say its 32 degrees farenheit outside, and your diving in a heated swimming pool where the water temp is 86 degrees F. Are you saying the warm water isnt insulating you from the cold air temperature? The only difference here is scale. Yes, the water is always conducting heat away from you (assuming water is colder than body temperature), but at the same time it is also insulating you from the colder air or water around you. In the case of a wetsuit the heated water in your wetsuit helps to insulate from the colder water outside your wetsuit, while at the same time...the colder water is conducting heat away from the warmer water. Air is a conductor too....just not as good as water because its not as dense...Its all relavent.

 

[bradshsi]

Its both an insulator AND conductor. Any level or space that separates your skin from the cold water or cold air is an insulator, regardless how thin.

In the case of a wetsuit the heated water in your wetsuit helps to insulate from the colder water outside your wetsuit, while at the same time...the colder water is conducting heat away from the warmer water. Air is a conductor too....just not as good as water because its not as dense...Its all relavent.

As you note, every material conducts to some degree. However in the scheme of things the water between your skin and the neoprene of the suit has no real insulating contribution.

The conductivity of water is about 0.614 W/mK
The conductivity of neoprene foam is about 0.038 to 0.060 W/mK

So the foam is 10 to 16 times better at insulating. Now when you take into account the thickness the difference really stands out.

Assume a 0.5mm layer of water next your skin and a 3mm wetsuit.

The relative insulating capacity of the neoprene watsuit to the water is then
(0.614/0.5) / (0.0380/3) = 97

So for all practical purposes the insulation contribution of this water is insignificant.



As a further note, I agree with what spectrum (Pete) says regarding air vs water next to your skin. Since air has a conductivity of 0.026 W/mK it would be better to have air instead of water. However since the layer would be so thin, the improvement in insulation would be small. Of course this neglects heat loss due to water circulation which can be a significant problem.

All in all the conclusion is that a close fitting suit is your best defense against heat loss.

 

[spectrum]

Nice job on the thermal data bradshsi

As for the heated swimming pool analogy your body did not heat the pool. As a body of heated water it will shelter you from the cold air but it is still sucking heat from your body 25 or so times faster than air of the same temperature.

As for the water in your suit it just readilly accepts your body heat and presents it to the next surface, the inside of your suit.

Worse yet if the water is of any appreciable volume it will migrate thorugh the suit and disperse your energy for loss. Even worse the mere act of swimming creats a peristaltic action that attempts to exchage that heated water for ambient through every opening in the suit.

Pete