drysuit, and BCD for buoyancy?

Jeff Pack · Post by **Jeff Pack** » Sun Oct 23, 2011 1:14 am

I was curious, what is the reason for when diving with a drysuit, to not use the BCD for buoyancy, instead of just the suit?

Seems to me its easier to release air from the bcd, than the suit.

Linedog · Post by **Linedog** » Sun Oct 23, 2011 4:07 am

For me I only have to think about one BCD underwater. In case of a rapid assent I only have to vent from one place.

Alexitt · Post by **Alexitt** » Sun Oct 23, 2011 5:47 am

You're likely to get a bunch of differing opinions on this one... Personally I keep just enough air in my suit to keep the squeeze off and use my bc for bouyancy, but I dive a Bare D6 Neoprene suit that's fairly bouyant and takes minimal air to be comfy... I think it's going to come down to trying it a few different ways and using what's most comfortable for you...
My 2 psi...

Grateful Diver · Post by **Grateful Diver** » Sun Oct 23, 2011 6:00 am

The "runaway ascent" scenario is a false logic ... because the drysuit dump valve is designed to release air much more slowly than BCD vent valves do. In the runaway ascent situation, as you approached the surface you can more easily reach a point where the air in your suit would be expanding faster than you could dump it. Using the BCD for buoyancy gives you a much better chance to avoid finding yourself on the surface prematurely.

As for controlling two air sources, consider what happens when you raise your inflator hose ... it puts the dump valve on your drysuit right where it wants to be in order to vent air. If you dive with your dump valve in the automatic open position, the air will dump from your drysuit as you vent your BCD without you doing anything. This is why drysuit dump valves are typically placed on the same side as your BCD inflator hose.

Consider that whatever air is in your suit will move as you move. The more air you put in your suit, the harder it is to control where that bubble's going to go ... which could be particularly problematic if it ends up in your feet. If you should find yourself in that runaway situation, the BCD gives you a vent valve on the bottom of the air cell, so you can vent while inverted. The only drysuit on the market that gives you that option is the Apollo suit, which has dump valves in the ankles.

Also consider that the air cell in your BCD presents a much smaller "container" for the air to migrate, and is designed to accommodate this movement. Managing the air in your BCD is easier than in your drysuit, because it has less places to go.

For those reasons I recommend to use the BCD for buoyancy control, and only put enough air in the drysuit to add some loft to the undergarment.

Now, there is a caveat here which is that for the adequately experienced, properly weighted diver, there isn't going to be much difference either way ... because you won't be using very much air regardless of where you put it. For the inexperienced or improperly weighted diver, it will make a more significant difference.

... Bob (Grateful Diver)

Alexitt · Post by **Alexitt** » Sun Oct 23, 2011 6:15 am

Yeah... What Bob said...

Linedog · Post by **Linedog** » Sun Oct 23, 2011 6:46 am

OK, I was just schooled.

Jeff Pack · Post by **Jeff Pack** » Sun Oct 23, 2011 7:17 am

thx Bob, that was pretty much my thoughts as well, but being new, I wanted to ask in case there was some reason I wasn't considering.

Dusty2 · Post by **Dusty2** » Sun Oct 23, 2011 10:42 am

I would never disagree with Bob on an issue with anything diving related as to how it relates to new or inexperienced divers. I will add to his caveat though. As you become more experienced you will gravitate to what works best for you and issues like inversion become non issues. I personally only use my BCD at the surface and use my suit exclusively underwater but this is a personal choice and depends on getting everything in balance and developing an inner sense of when and how to add or vent air. I would highly recommend you go with Bobs words of wisdom at least until you have arrived at the point where everything begins to become automatic and you need not think about it to make it happen. Then you can play around and see if something else works better for you.

Geek · Post by **Geek** » Sun Oct 23, 2011 12:13 pm

I would add to what dusty said.. When you get more exp you usually drop the amount of weight you need to get under, then when your weighting is spot on you might find the BCD a bit much for fine control and stick with the drysuit while at depth, basically the goal being that taking the squeeze out of the suit=the bouency needed.. My 2psi

LCF · Post by **LCF** » Sun Oct 23, 2011 12:47 pm

I started out, as taught, trying to use the dry suit for buoyancy, and ended up with a couple of rather nasty uncontrolled ascents (one from 70 feet). When I took Fundies, Steve taught me to put only enough gas in the suit to relieve squeeze, and use the BC for primary buoyancy control. I was not as warm, but much more stable in the water that way. I also learned that, if you do that AND your weighting is pretty spot-on, it works best to vent the BC as you begin your ascent, and allow the gas in the suit to expand a bit before you begin venting the suit. It's much easier to move the gas around and get it to the dump valve, if you are not trying to squeeze every tiny molecule out of your undergarments.

As I got more experience, I got better at managing more gas in the suit. Nowadays, I put gas where it makes sense. If I'm going to be going through swimthroughs or otherwise assuming unusual attitudes in the water, I minimize gas in the suit. If I'm diving in very cold water, I maximize gas in the suit to stay warm. If I need to put gas in a certain place to balance myself better, I put it where it works. I don't have problems any more, figuring out which space needs venting. Eventually, you learn to feel the weight of your rig on your back (and when it starts to lift) and how loose or tight the suit feels, and you'll just know which one is getting to need venting.

Jeff Pack · Post by **Jeff Pack** » Sun Oct 23, 2011 9:08 pm

My first dive today, I only used the BC, 2nd dive BC/Suit. Can get abit finer control with suit I felt. But basically used suit just to take care of squeeze, and fine tune buoyancy once and awhile.

BASSMAN · Post by **BASSMAN** » Sun Oct 23, 2011 10:10 pm

In my own Preference, I use my Suit air, for buoyancy control and added warmth. I use my BC on the surface or if I'm recovering a 10 lb. down rigger ball, I will add the extra air needed in my BC.

Joshua Smith · Post by **Joshua Smith** » Sun Oct 23, 2011 11:02 pm

Grateful Diver wrote:The "runaway ascent" scenario is a false logic ... because the drysuit dump valve is designed to release air much more slowly than BCD vent valves do. In the runaway ascent situation, as you approached the surface you can more easily reach a point where the air in your suit would be expanding faster than you could dump it. Using the BCD for buoyancy gives you a much better chance to avoid finding yourself on the surface prematurely.

As for controlling two air sources, consider what happens when you raise your inflator hose ... it puts the dump valve on your drysuit right where it wants to be in order to vent air. If you dive with your dump valve in the automatic open position, the air will dump from your drysuit as you vent your BCD without you doing anything. This is why drysuit dump valves are typically placed on the same side as your BCD inflator hose.

Consider that whatever air is in your suit will move as you move. The more air you put in your suit, the harder it is to control where that bubble's going to go ... which could be particularly problematic if it ends up in your feet. If you should find yourself in that runaway situation, the BCD gives you a vent valve on the bottom of the air cell, so you can vent while inverted. The only drysuit on the market that gives you that option is the Apollo suit, which has dump valves in the ankles.

Also consider that the air cell in your BCD presents a much smaller "container" for the air to migrate, and is designed to accommodate this movement. Managing the air in your BCD is easier than in your drysuit, because it has less places to go.

For those reasons I recommend to use the BCD for buoyancy control, and only put enough air in the drysuit to add some loft to the undergarment.

Now, there is a caveat here which is that for the adequately experienced, properly weighted diver, there isn't going to be much difference either way ... because you won't be using very much air regardless of where you put it. For the inexperienced or improperly weighted diver, it will make a more significant difference.

... Bob (Grateful Diver)

Bob is right on here. I will just add that I used my wing for buoyancy, and just added gas to my suit to take off squeeze, right up until I started diving my rebreather. I found out quickly that even a little gas in my wing yanks me into a vertical position on my ccr. The weighting is completely different. So, I learned to use my suit instead. The important thing is to figure out which method works best for you, and the gear you're diving in.

BASSMAN · Post by **BASSMAN** » Mon Oct 24, 2011 1:56 am

Joshua Smith wrote:The important thing is to figure out which method works best for you, and the gear you're diving in.

That about sums it up

Jeff Pack · Post by **Jeff Pack** » Mon Oct 24, 2011 9:31 am

thx, Just ordered a DUI Weight and Trim to help abit on weight balance as well. Also, Tried 3pd ankle weights. I know thats sort of frowned upon, but for learning, its helped abit, as I've always had floaty feet.

Joshua Smith · Post by **Joshua Smith** » Mon Oct 24, 2011 9:48 am

Jeff Pack wrote:thx, Just ordered a DUI Weight and Trim to help abit on weight balance as well. Also, Tried 3pd ankle weights. I know thats sort of frowned upon, but for learning, its helped abit, as I've always had floaty feet.

Good call on the weight and trim. I love mine!

eliseaboo · Post by **eliseaboo** » Mon Oct 24, 2011 10:26 am

Jeff Pack wrote:thx, Just ordered a DUI Weight and Trim to help abit on weight balance as well. Also, Tried 3pd ankle weights. I know thats sort of frowned upon, but for learning, its helped abit, as I've always had floaty feet.

I have floaty feet too, but damn if it doesn't make frog kicking a breeze!

Grateful Diver · Post by **Grateful Diver** » Mon Oct 24, 2011 12:20 pm

The ankle weights are a good investment ... when you get to the point where you decide you want to dive doubles you can cut the buckles off and they will make a nice 6# channel weight ...

... Bob (Grateful Diver)

RoxnDox · Post by **RoxnDox** » Mon Oct 24, 2011 8:43 pm

Grateful Diver wrote:The ankle weights are a good investment ... when you get to the point where you decide you want to dive doubles you can cut the buckles off and they will make a nice 6# channel weight ...

... Bob (Grateful Diver)

I have been kind of feet-heavy the last couple of dives with the new drysuit, so on Saturday I ended up using mine wrapped around the base of the valves (dive 1), then around the tank centered between the two straps on dive 2. Worked out pretty nice as a balancer...

Jim

Grateful Diver · Post by **Grateful Diver** » Tue Oct 25, 2011 6:46 am

Yup, they're a nice "quick fix" as trim weights too ...

... Bob (Grateful Diver)

Jeff Pack · Post by **Jeff Pack** » Tue Oct 25, 2011 7:03 am

Grateful Diver wrote:The ankle weights are a good investment ... when you get to the point where you decide you want to dive doubles you can cut the buckles off and they will make a nice 6# channel weight ...

... Bob (Grateful Diver)

With my back, I can safely say doubles will never happen. With a Steel 95, and 42pds of weight, thats pushing my back as is.

Although question, when I switch to my AL80's, how much weight do I add. I seem to recall about 4 pds?

CaptnJack · Post by **CaptnJack** » Tue Oct 25, 2011 7:28 am

+4lbs for an AL80 vs. most steel tanks which are basically neutral to -1.

+1 on the bad back although I am actually vastly more comfortable in doubles than a single. The larger weightbelt for singles makes me sorer.

skubi · Post by **skubi** » Wed Oct 26, 2011 3:47 pm

Jeff Pack wrote:With my back, I can safely say doubles will never happen. With a Steel 95, and 42pds of weight, thats pushing my back as is.

I've got a bad back too and the doubles can get really heavy even before you add on stage bottles. So I pretty much skipped the doubles route and went straight to a rebreather. My rEvo is about 75lbs ready to dive. I'm guessing that's a bit lighter than even your single tank setup - I know it was for me.

cardiver · Post by **cardiver** » Wed Oct 26, 2011 4:35 pm

42 lbs? Are you diving a 7 mm wet suit?

Jeff Pack · Post by **Jeff Pack** » Wed Oct 26, 2011 7:13 pm

cardiver wrote:42 lbs? Are you diving a 7 mm wet suit?

No Whites Fusion, Mk3 undergarment. Steel 95 tank.

36 Pounds and I was cork, Anthony suggested +6.

I might be a couple of pds heavy, but not alot.

Northwest Dive Club