Newbie questions regarding how wetsuits work

[t4e]

@ dfx - I've heard that some guys who are literally in freezing water use special tanks with exotic gases (argon?), which have better insulating properties than ordinary air.

i am no expert but from my readings, the argon is used in a separate tank only to inflate the drysuits when diving on trimix

 

[nimoh]

I believe semi-dry is somewhat of a misnomer. They have better wrist seals, ankle seals, neck seals and zippers that help to better restrict water exchange, and this helps you to stay warmer, although you still get wet.

---------- Post added April 13th, 2012 at 07:33 AM ----------

i am no expert but from my readings, the argon is used in a separate tank only to inflate the drysuits when diving on trimix

To the best of my knowledge, there isn't conclusive proof that argon is a significantly better insulator than air. However, helium is an extremely poor insulator, so if your main gas has a lot of helium, then you need a separate gas source for your suit, and most opt for argon since in theory it is a better insulator than air.

 

[dfx]

Ugh--I thought I understood, but now I'm not so sure again. If neoprene is impermeable to water, then I go back to my original question: Is there not another impermeable material that's a better insulator than neoprene? You could line an impermeable exterior with just about anything.

Sure you can. The problem with that approach is that even the slightest rip in the impermeable exterior will cause the insulating interior to flood with water and thus lose its insulating properties. Neoprene is not only impermeable, it also doesn't soak up any water even when it's damaged.

Basically, in order to stay warm, you need to drape yourself in gas and keep that gas in place. That's what clothing does on land (and also blankets). But those materials tend to soak up water, which will replace the contained gas and so make them cold. Neoprene doesn't do that.

Also, what about so-called "semi-dry" suits? I thought the whole point of those was that they had seals at the wrists, ankles and neck that inhibited entry of water? That would only make sense if the suit allowed water to enter through some other means--like saturating through the walls of the suit. If a semi-dry suit is effectively sealed, and there is (inevitably?) air trapped inside, then you'd have the same issue as with a dry suit. This is another reason why I was under the (mistaken?) impression that neoprene is semi-porous.

Semi-dry suits work the same way as regular wetsuits, the improved seals don't keep the water from entering, they only keep it from circulating more once it has entered. You want water to enter the suit, but want to keep it in place once it's there.

Only drysuits are really sealed against entry of water, and because of that, you need some kind of inflator (and deflator) attached to them. Some drysuits are made out of neoprene.

 

[Crush]

Curious to know the difference between air compressing to the pressure of the water around it vs. water at the same pressure. Why would air cause bruising, but replacing it with a "incompressible fluid" (it is, just not for our purposes here) wouldn't?

The air does not pinch you - the suit does when the air is compressed. This doesn't always happen, but it can. The pinching depends on how well the suit fits you, among other things.

Ugh--I thought I understood, but now I'm not so sure again. If neoprene is impermeable to water, then I go back to my original question: Is there not another impermeable material that's a better insulator than neoprene? You could line an impermeable exterior with just about anything.

Neoprene is a good balance between durability, insulation, and flexibility. You could make your own wetsuit out of a novel material, but neoprene is pretty darn good. The problem with an impermeable exterior is that if the interior is not water-proof a small tear will ruin your suit's insulative properties (water will rush in, and water conducts heat quite well). Neoprene is wonderfully dumb technology which survives most forms of damage - you can rip one sleeve off your wetsuit and still use it during a dive.

@ dfx - I've heard that some guys who are literally in freezing water use special tanks with exotic gases (argon?), which have better insulating properties than ordinary air.

The heavier the molecule the gas the less efficiently it conducts heat. Argon is much heavier than nitrogen and oxygen, so it will insulate better. I often joke that I am going to market uranium hexafluoride (UF6) as a new suit gas for tech divers. BTW, heavier gases will increase breathing resistance, which is why we use light gases in trimix (helium).

 

[acrofrag]

Boyle's law dictates that a gas under double the pressure shrinks to half its volume. An air bubble trapped in your wetsuit thus has half its volume at 10 meters depth than it had at the surface. Since none of the surrounding materials (wetsuit, your body, water) shrink in the same manner (they're all incompressible), that shrinking air bubble can produce a suction cup effect under the right circumstances, for example at a fold in your suit.

Yes, but again, how is that different than water at the same pressure. Air doesn't compress itself for no reason!

 

[rhwestfall]

I often joke that I am going to market uranium hexafluoride (UF6) as a new suit gas for tech divers.

dang, beaten (again) to the punch. check that one off the "I got a great idea, and I'm going to be rich" list......

 

[dfx]

Yes, but again, how is that different than water at the same pressure. Air doesn't compress itself for no reason!

Ambient pressure! Gases compress (shrink, lose volume) under pressure, liquids and solids don't (well they do a tiny bit, but that's negligible). Unless some substance or material is contained within a rigid, sealed container (like, say, in a scuba tank), that substance or material will be subjected to the same pressure as everything around it, which is the ambient pressure. In other words, when you're 10 meters under water, your whole body, everything inside you, everything on you, all solids, liquids and gases in and around you will be subjected to the ambient pressure of down there, which is twice the pressure than at the surface. The only exceptions would be gases within a rigid, sealed container.

No offence, but that's the stuff you learn in your basic OWD course, isn't it? How can you have 500+ dives and not know why a gas under pressure (under water) compresses? After all, it's why you have to equalize your ears when you descend and it's why you're not supposed to hold your breath.

 

[300bar]

It isn't even the rubber in the neoprene that keeps you warm -- it's the gas bubbles trapped in it. The useful nature of neoprene is that it traps bubbles in an insoluble and impermeable substrate, so that you can immerse the stuff without the gas being displaced by water. The thicker the neoprene, the more insulating capacity it has.

The ideal wetsuit admits as little water as possible, just enough to fill the air spaces, as described. It then minimizes the exchange of that water with the water in which you are diving, so that you expend only the heat you have to to warm that first bit, and don't continue to lose heat to water that then is lost to the ocean.

A perfect neoprene wetsuit is a neoprene dry suit ( ), but then you do need to add a little air to avoid squeeze. Neoprene dry suits are very warm in shallow water.

And this is the only correct answe sofar, it the gas in the neoprene that keeps you warm.
The less water enters, the warmer you will be.
Try to get a good specialty on neoprene and you will learn the diference.
Dive suits are a compromise, bigger cels will give more insulation, but they will float more.
So surfsuits have bigger (gas)cells and are warmer but the FLOAT.
Divesuits have a somewhat smaller cell but need less weight to get down.
Compresed neoprene is only good for drysuits, because the cell are to small.
Crussed neoprene is a dumb idea all the way. Crussed aka boken cells, just think about it.

edit: had to add. I HATE neoprene drysuits.

 

[elan]

The water isn't warming you, you are warming up the water!

It depends on what kind of water we are talking about. Double distilled oak aged warms me up pretty well

 

[elan]

I believe semi-dry is somewhat of a misnomer. They have better wrist seals, ankle seals, neck seals and zippers that help to better restrict water exchange, and this helps you to stay warmer, although you still get wet.

Thats a TLS description?