Drysuit squeeze.

[freeclimbmtb]

For some reason, I continue to struggle with the concept of why this happens. I dive a drysuit and am familiar with the squeeze you get as you decend. As you pump air into it, the squeeze is relieved...but WHY? 1 ATM on the surface your comfortable, 33 feet, 2 ATM its a little tight, 66 feet 3 ATM, suddenly you dont have the mobility to add air... How come this happens with the drysuit but not neoprene...or on bare skin? or boardshorts? There is no difference in pressure from one material to the other...the water column remains unchanged. If someone stands on your shoe, it hurts...if they stand on a pillow on your shoe...it hurts less...fine. But then if they stand on your bare foot, that hurts too! Ive kind of just accepted that it works the way it works, but every once in a while I try to reason through it and feel like I am missing a simple answer.

 

[oly5050user]

For some reason, I continue to struggle with the concept of why this happens. I dive a drysuit and am familiar with the squeeze you get as you decend. As you pump air into it, the squeeze is relieved...but WHY? 1 ATM on the surface your comfortable, 33 feet, 2 ATM its a little tight, 66 feet 3 ATM, suddenly you dont have the mobility to add air... How come this happens with the drysuit but not neoprene...or on bare skin? or boardshorts? There is no difference in pressure from one material to the other...the water column remains unchanged. If someone stands on your shoe, it hurts...if they stand on a pillow on your shoe...it hurts less...fine. But then if they stand on your bare foot, that hurts too! Ive kind of just accepted that it works the way it works, but every once in a while I try to reason through it and feel like I am missing a simple answer.

Go back to your open water course materials,if a PADI course info is in module 1...
Boyles law...air in suit increases in density during descent,decreases in volume. Same happens in wetsuit as neoprene density increases and its volume (thickness)decreases. Also as volume decreases buoyancy decreases.

 

[scc135]

Water is technically compressible from a physics standpoint but the compression applied from depth pressure to water doesn't compress enough for you to feel it. Air compresses easily, so you feel that squeeze but not in a neoprene wetsuit.

 

[mmerriman]

simply put - the board shorts and the wetsuit compress - however they compress into themsleves. The drysuit makes you part of a closed container - when it compresses, you get comressed in it.

 

[freeclimbmtb]

Go back to your open water course materials,if a PADI course info is in module 1...
Boyles law...air in suit increases in density during descent,decreases in volume. Same happens in wetsuit as neoprene density increases and its volume (thickness)decreases. Also as volume decreases buoyancy decreases.

Boyles law doesnt help me with this, not from PADI and not from my fluid dynamics classes in school.

simply put - the board shorts and the wetsuit compress - however they compress into themsleves. The drysuit makes you part of a closed container - when it compresses, you get comressed in it.

Thats the simple answer I was overlooking. Got it now.

 

[Hawkwood]

simply put - the board shorts and the wetsuit compress - however they compress into themsleves. The drysuit makes you part of a closed container - when it compresses, you get comressed in it.

Nicely put. For those who can't visualize, think about what happens to an air-filled plastic pop bottle when you take it down - that's how the suit "reacts"

 

[freeclimbmtb]

Nicely put. For those who can't visualize, think about what happens to an air-filled plastic pop bottle when you take it down - that's how the suit "reacts"

Right. The bottle collapses on itself and contacts you inside...as you pump air in, you restore shape of the bottle and get rid of that contact.

 

[Scott]

Boyles law doesnt help me with this, not from PADI and not from my fluid dynamics classes in school.

Boyles law is not unique to PADI.

Right. The bottle collapses on itself and contacts you inside...as you pump air in, you restore shape of the bottle and get rid of that contact.

Just remember to the vent the dry suit on your ascent. The cap may pop off the bottle but more serious things will happen to you if you don't.

 

[Blackwood]

.Thats the simple answer I was overlooking. Got it now.

Except that's not particularly apt. The compression of board shorts (which is likely so minuscule as to be unmeasurable) due to increased pressure has little to do with anything.

Boyles law absolutely applies. You have to equalize a drysuit but not a wetsuit for the same reason you equalize your ears but not your foot.

33 feet doesn't feel differently than does 66 feet other than in your air pockets, which is why only they must be equalized.

You're feeling the suit, as cushioned by the volume of air inside it. If you stood in your suit on the surface and vacuumed out enough air that the suit fit as tightly as it would at 3 atmospheres of depth sans added air, it would feel the same as being at that depth. Conversely, if you fill your drysuit with water, you won't have to equalize it as you vary depth, even as a closed system.

 

[decompression]

Also, consider the differences in what's being compressed.....a hi loft, air filled undergarment to a thick rubber wetsuit to water filled board shorts....you are sealed in the drysuit and therefore being squeezed by the sealed suit ( love the bottle analogy.)