Correct Bouyancy Control Dry Suit

[BGF]

BC for buoyancy, ds for anti squeeze, valve turned 1-2 turns closed. I like the arm pumping move described by cldwdiver. Never had a problem venting but that would help push it out faster if needed

 

[Divin'Papaw]

Where is option 3? Leave the drysuit valve open (or mostly open) the entire dive, and let it vent itself on ascent?

Maintaining buoyancy with the drysuit is asking for trouble. One day you'll blow the ascent, and there will be no stopping it.

But, it's your life. You choose.

This is my preferred method by far. There are times I'll need to orient my body to foster suit venting on ascent (roll slightly to the right and raise left arm chicken wing fashion), but most of the time the expanding gas vents on its own. The only time I vary this is if I find I'm cold. I'll dial the exhaust vent down a notch or two and add a bit more air into the suit while also venting some from my wing. I don't like the way this feels as much as my suit feels too loose, but it is nice when I'm getting chilled.

 

[Divin'Papaw]

* Do not push the valve button. It will usually let a little water in. Adjust how open the valve is for ease of venting. Roll your valve-side shoulder up, lift your arm toward the surface, allow air into it, then flex your arm to pump the air out the valve. Repeat as needed. Sometimes you need to raise your torso to get air up into your arm.

I call this the "chicken wing".

I never ever push my exhaust valve.

 

[spt29970]

Rob, I seem to be in the minority, but I do what you do. I use my drysuit for both buoyancy and warmth. Here is question I have never had answered from those that use the BC for buoyancy. If you have to put air in the BC during the dive to maintain neutral buoyancy, why don't you take some weight off of your weight belt until your BC is empty? Another way of putting this is that the amount of air needed to puff up the drysuit insulation should be all the air you need to maintain neutral buoyancy. If not, you are carrying too much lead.

In my opinion, the only reason to use the BC to is compensate for the weight change in the tank during the dive. For a single tank recreational dive, this is only 5lbs. The amount of air needed to compensate this is about 2l. When distributed over the entire drysuit volume, this makes a relatively trivial change to its inflation. The story is different if you are doing technical diving and are carrying a lot more air. If diving twin 130s, you are carrying 20lbs of air. Using your drysuit to add an extra 20lb of lift would seriously overinflate the suit. Using the BC would be a much better idea. Even in this case though, the goal should be to end the dive at 15ft with a correctly inflated drysuit and no air in the BC.

As far as the vent is concerned I adjust the tension during the dive. I leave it mostly open, but close it partially when I am at depth to avoid unintentional venting. When I am ready to ascend I open it all the way. On the surface I inflate the BC. I also close the vent all the way and add a little air to keep warm while swimming back to boat. I never push the vent button except when burping the suit before the dive.

 

[Divin'Papaw]

Rob, I seem to be in the minority, but I do what you do. I use my drysuit for both buoyancy and warmth. Here is question I have never had answered from those that use the BC for buoyancy. If you have to put air in the BC during the dive to maintain neutral buoyancy, why don't you take some weight off of your weight belt until your BC is empty? Another way of putting this is that the amount of air needed to puff up the drysuit insulation should be all the air you need to maintain neutral buoyancy. If not, you are carrying too much lead.

In my opinion, the only reason to use the BC to is compensate for the weight change in the tank during the dive. For a single tank recreational dive, this is only 5lbs. The amount of air needed to compensate this is about 2l. When distributed over the entire drysuit volume, this makes a relatively trivial change to its inflation. The story is different if you are doing technical diving and are carrying a lot more air. If diving twin 130s, you are carrying 20lbs of air. Using your drysuit to add an extra 20lb of lift would seriously overinflate the suit. Using the BC would be a much better idea. Even in this case though, the goal should be to end the dive at 15ft with a correctly inflated drysuit and no air in the BC.

As far as the vent is concerned I adjust the tension during the dive. I leave it mostly open, but close it partially when I am at depth to avoid unintentional venting. When I am ready to ascend I open it all the way. On the surface I inflate the BC. I also close the vent all the way and add a little air to keep warm while swimming back to boat. I never push the vent button except when burping the suit before the dive.

To be neutral at the end of your dive you need to be negative by the weight of your gas otherwise you can't hold your stops. During the entire dive, up until the end, you are by necessity diving negative without taking into account any buoyancy device. The question is, where are you going to put the air to offset the negative buoyancy of the air in your tank(s)? Most of us prefer the BC. The air in the drysuit is to keep the squeeze off and keep you warm. It's alot easier to manage the bubble you need to offset the negative buoyancy of the air in your tank(s) if it's in your BC than if it's in your drysuit.

I think we pretty much agree, I'm just perplexed by the comment that if you have to put air in your BC you need to take weight off. If you're properly weighted, the air your putting in your BC is to offset essentially the weight of the compressed air in your tank.

 

[spt29970]

To be neutral at the end of your dive you need to be negative by the weight of your gas otherwise you can't hold your stops.

That is essentially what I said. If you are neutral at the end of the dive, with correct inflation of the suit, you are negative at the beginning. For a typical 80ft tank, that means that you are about 5lb negative at the beginning. This requires and extra 5lb of lift somewhere. You can put it in the BC, but then you have the extra task loading of managing two airspaces, or you can put it in the suit, where it makes a relatively trivial change to the suit inflation which I find easier to manage. Remember just breathing induces +-5lb of buoyancy change. If you have a lot of gas, you then you have to use the BC.

The problem I see is that many drysuit divers carry too much lead. Then they have no choice but use the BC to lift the lead in addition to the air.

One final comment is that I put a high value on reducing task loading. Perhaps that is because I usually dive with my camera, so both hands are usually occupied.

 

[fppf]

I pratice both ways, if I blow out a BC the drysuit is my backup control.

Normal diving, little air in the suit and control with the BC.
I never touch the drysuit vent during a dive, I set it about .5 turns from full open.

I also dive with a DLSR with strobes, run reels, mark the moring line, ect. Task loading takes practice, practice, practice.

My camera is really negative, but I don't drop any weight just in case I drop the thing. This means I dive on the heavy side. I would not want to dive with all that air in my Drysuit on a regular baisis.

 

[spt29970]

My camera is really negative, but I don't drop any weight just in case I drop the thing. This means I dive on the heavy side. I would not want to dive with all that air in my Drysuit on a regular baisis.

Try making your camera less negative. I use capped PVC pipes as floats. Some people various closed cell foams. You don't want your camera to change your overall buoyancy. Besides, it is much easier to operate if it is near neutral. Sorry about the thread hijack.

 

[gorcio]

1) Take the squeeze off with the dry suit and mainatain bouyancy with the BCD.
2) Use the Dry Suit for all bouyancy control. Close the Dry suit valve at the surface and open it only when ascending. On Ascent control venting by lowering and rasing you arm (i.e. the vent valve).

From what I have experienced with mine, and from what I can see others doing :
1. use BC/wing for buoyancy, DS for thermal comfort and as secondary (emergency) buoyancy unit if main one fails.
2. Once You start adding more equipment like twin tanks, stage tanks etc, You will realize that it would take quite a lot of air to pump into Your dry suit to compensate and it is asking for a problem.
3. why would You keep the release valve in any scenario completely closed ? I keep mine 1/3 closed , most of my buddies close it up to 1/2.

 

[String]

If you're a single tank AND your weighting is correct you can quite happily use the suit or the wing/bc for buoyancy.

The suit stops being viable once you start diving overweighted - usually from carrying multiple tanks.