Using a Drysuit for Buoyancy Control

[Rick Murchison]

There's a substantial difference in the behavior of drysuits depending on their construction, and so a substantial difference in how they appear to be used on a dive. A diver who is properly weighted in a shell suit will find that aside from the gas needed to maintain proper loft in his underwear, very little use of the BC is required (beyond corrections for gas consumption over the course of the dive). That's not to say the drysuit is being used for buoyancy control, just that with a shell suit, which doesn't change its own buoyancy with depth, there isn't much need to use the BC, so it may appear that the drysuit is what's being used as that's the only place you need to add gas as you descend... with a neoprene suit, however, the BC will (should!) see a lot of use as the suit itself loses buoyancy as you descend, and you'll need to add gas to the BC to compensate as well as add gas to the drysuit to maintain proper loft in the undergarment.
Bottom line - as others have already said - gas should be added/removed from the drysuit as needed to maintain proper underwear loft; gas should be added/removed from the BC to maintain proper buoyancy.
Rick

 

[rogerhelmich]

just a little squeeze will do. Use the BC!! You'll be glad you did

 

[TecDiver1990]

Personally, I only put air in my drysuit to control squeeze. There is a reason we wear those things called "Buoyancy Control" Devices. But it's all diver preference. My buddy uses his for buoyancy control.

If you're more comfortable doing it one way over the other, then do it.

 

[D_B]

Couple of things not mentioned here ...
Some use their suit for buoyancy to stay warmer .. with the minimal amount of weight necessary, the amount of air in the suit is not going to overly large (I've seen that in my friends drysuit uses less weight than with a thick wetsuit)
Also , in training to dive a drysuit , using only the suit for buoyancy, slightly overweighted, in a pool at 8ft ... if you can handle a feet up, stuck inflater on for 3 seconds before your released drill , disconnect, vent, turn upward, pull open neck seal, in hood and gloves, and all done without reaching the surface .. then your better prepared for anything that happens at depth , no matter what method you decide to use for buoyancy control
.. there are pluses and minuses to everything

 

[Thalassamania]

We do this one every few months.

1. If you keep the level of squeeze constant through the dive you will also keep your buoyancy constant through the dive. Except for the loss of weight as a result of gas consumption ... but that's what your BC or BP/w is for.
2. If you do not use your BC or BP/w to compensate for you gas consumption, you will have to increase the level of squeeze through the dive and if you start off properly shrink wrapped, that's going to get damned uncomfortable by the end of the dive.
3. If you attempt to use your BC or BP/w to compensate for suit and bc compression ... the squeeze is gonna get ya, real quick.

So on descent you need to add air to your suit to keep the squeeze constant and you need to add air to your BC or BP/w to make up for compression of the air that was in the BC or BP/w to balance out the weight of your gas. On ascent you need to vent both appropriately. Through the dive you need to reduce the air in your BC or BP/w as you use up gas.

 

[Ben_ca]

I guess nothing much has changed in 6 years... Nice to see Uncle Pugs answers... He was always wise and kind.

 

[TSandM]

I think the goal is to be able to do either, according to what you want to do on a given dive. In caves, where the diver's attitude is prescribed by the direction of the tunnel, I want a squeezed suit so I don't have tons of air going to my feet when I have to go head down. In very cold open water, I want as much air in the suit as I can comfortably manage, to keep me warm. I can put gas in whichever space I want, and even transfer it from one to another during a dive if conditions make that desirable.

I think it's easiest for NEW drysuit divers to minimize the gas in the suit, because suits are slow to vent and you can get into trouble very quickly. But as you get more comfortable (and assuming you have a properly constructed suit that you CAN vent) you can make your own decisions about where the gas is best put.

 

[Doc Harry]

I think the goal is to be able to do either, according to what you want to do on a given dive. In caves, where the diver's attitude is prescribed by the direction of the tunnel, I want a squeezed suit so I don't have tons of air going to my feet when I have to go head down. In very cold open water, I want as much air in the suit as I can comfortably manage, to keep me warm. I can put gas in whichever space I want, and even transfer it from one to another during a dive if conditions make that desirable.

+1 for me

I think it's easier for new divers to use the BC for buoyancy control, nothing screws you up more than having a huge bubble of air go to your feet.

 

[Thalassamania]

Except not having enough air in the suit and squeeing the bejesus out of your you-know-whats!

 

[Doc Harry]

Except not having enough air in the suit and squeeing the bejesus out of your you-know-whats!

You are correct!