BCD use while diving drysuit ...

Question for drysuit users....

When you are diving drysuit, how much of buoyancy do you control with drysuit air and how much through pumping air into your BCD? I believe I read somewhere on these forums that you should control your buoyancy purely through Drysuit and use BCD when it isn't enough. I cant find that post. With only 6 drysuit dives I am thinking if it would make more sense to dive with a slightly squeezed drysuit just to give a more streamlined "wetsuit-like" profile. The air bubble management should also be easier with as little air in Drysuit as possible. Or am I wrong?

Thanks in advance

You have it right. BC for Buoyancy Control, drysuit for thermal control. Youy are also correct when you talk about bubble managment, which is the reason why you do not use your suit for buoyancy control. In emergencines , if you lose buoyancy control from your BC then you can use your drysuit.

Jim

ironically (maybe not) there are agencies that teach it different ways. I only use my DS for thermal management.

P.S. - slightly squeezed can be painful.....

When I first started diving dry, I would put as much air in my drysuit as was comfortable (which was a trade-off between not being squeezed, being warm enough, and still feeling in control). The rest of my buoyancy was taken care of by using my wing.

Now that I'm comfortable in a drysuit, I tend to run a lot more gas in it....to help keep me warm. In a single cylinder, I very rarely put gas in my wing. In doubles, my drysuit alone is not enough to offset the amount of weight I have on me.


Since you're still new to the drysuit, I'd suggest using whatever is comfortable....don't squeeze yourself so tight that it hurts and you're freezing....but also don't try to use just the drysuit for buoyancy if you feel like you're on the edge of losing control. It will get better as you get more comfortable!

rhwestfall:

ironically (maybe not) there are agencies that teach it different ways.

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I believe the stated reasons for that policy are concerned with the potential 'complication' faced by a new drysuit user in having to handle two variable buoyancy sources on ascent - and the consequent risk of rapid, uncontrolled rise to the surface.

Some agencies teach the use of the dry suit for buoyancy control, because it minimizes task-loading on the diver. Some teach using the BC for buoyancy control, and only putting enough air in the dry suit to relieve squeeze. I am generally in favor of the latter approach for more novice divers (for the simple and egocentric reason that it worked better for me ). The dynamic instability of the gas bubble in the dry suit can result in some nasty problems, when a new diver is not accustomed to managing it. I did a ballistic ascent from 70 feet early on, and had a recently certified student do one from 50 feet, despite me hanging onto her the whole way (you CAN'T dump somebody's dry suit for them!).

However, I do not believe there should be a hard and fast rule. Once you are facile enough with the dry suit to manage the bubble, put the air where it's easiest for that dive. For cave diving, where we frequently assume "unusual attitudes", I run my suit squeezed. Cold isn't a big issue, but swimming for a half hour with feet full of air, because I can't find a safe place to drop them enough to get it out, is a nuisance. On the other hand, winter open water diving in Puget Sound will find me with as much air in the dry suit as it will retain, in an effort to maximize the insulating power of the suit and undergarments.

Theres two different schools of thought on this..
1. Use the drysuit only
2. Use the BC for bouyancy and only remove squeeze.
Neither is wrong, neither is right.

HOWEVER, for a single tank, properly weighted diver - theire both the same..
If you have the proper ammount of weight, youll only need to have enough air in the suit to be comfortable and then you got rid of the whole topic of what device to choose for bouyancy.

As others has mentioned, with doubles youll need to add some in the BC because of the added weight


TSandM: you CAN infact dump someones drysuit for them given they are head up. Itll be a semidry suit afterwards though..

In cold water, I use my drysuit almost exclusively since the more air I have in it, the warmer I tend to be. My weighting is as such that I really don't need my BC. In warmer climates when diving dry, it is a combination of the two based on my comfort. It is just a pain to have to vent both the suit and the BC upon ascent. It is also easier to let a specific amount of air out of a BC than it is a drysuit.

+1 for drysuit for squeeze and BC for bouyancy (but very minimally).

jar546:

It is also easier to let a specific amount of air out of a BC than it is a drysuit.

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I beg to differ. With a properly functioning and adjusted drysuit exhaust valve, one can dump gas with a great amount of control...and hands-free.
In my opinion, ascents are much more conveniently managed by a gentle roll of the shoulders (method for exhausting gas from a drysuit exhaust valve located on the upper left arm) than having to use a hand to yank on a dump valve or to hold the power inflater assembly at the highest point in the water column then hit the exhaust button.

@CAPTAIN SINBAD: The two methods of using a drysuit are both valid.

A beginner drysuit diver will find it easier to manage the drysuit bubble if he runs a minimal amount of gas inside the drysuit (just enough to offset squeeze) and uses the BCD to manage the rest of his buoyancy. Understand that this will entail managing two buoyancy devices during ascent.

It's common for novice drysuit divers to be so afraid of an uncontrolled ascent that they don't run enough gas inside the suit to offset squeeze. This results in drysuit hickies, restricted limb movement, and being cold. Try to avoid this pitfall.

If you are diving a single tank setup, you'll find that the amount of gas needed to offset squeeze in your drysuit is just about the right amount to manage your buoyancy. On my typical single-tank local dives here in SoCal, I use my drysuit exclusively to manage buoyancy underwater. On the surface, during the kick out on shore dives, I inflate my BCD quite a bit and also add a little extra gas to my drysuit so that it's really easy to kick while on my back.

As you become more comfortable using your drysuit, I recommend that you experiment using both methods of managing buoyancy (drysuit only or drysuit + BCD). As others have pointed out, there will be situations when it's appropriate to use one method over the other.