dry suit buoyancy

[DiverLaura]

If you are properly weighted, and using the BC to offset the gas in your tanks, using your drysuit for neutral is no problem whatsoever. That is essentially what all you who say "use drysuit inflation only for relieving squeeze" are doing. You put some in the BC to offset tanks, add a little at depth because what is in your wing has compressed, and use your drysuit to keep you warm and not squeezed. In doing that, you ARE in fact using your drysuit for part of your buoyancy control. You should not have so much weight (if just diving single tank) that you need a huge amount of gas in either DS or BC. If you do, you are probably diving heavy.

This is the finesse of drysuit diving. Using BOTH BC and DS.

Wings = gross buoyancy management
Drysuit = "not squeezed" puts you darn close to neutral
Lungs = fine tuning

 

[Thalassamania]

If you are properly weighted, and using the BC to offset the gas in your tanks, using your drysuit for neutral is no problem whatsoever. That is essentially what all you who say "use drysuit inflation only for relieving squeeze" are doing. You put some in the BC to offset tanks, add a little at depth because what is in your wing has compressed, and use your drysuit to keep you warm and not squeezed. In doing that, you ARE in fact using your drysuit for part of your buoyancy control. You should not have so much weight (if just diving single tank) that you need a huge amount of gas in either DS or BC. If you do, you are probably diving heavy.

This is the finesse of drysuit diving. Using BOTH BC and DS.

Wings = gross buoyancy management
Drysuit = "not squeezed" puts you darn close to neutral
Lungs = fine tuning

Exactly.

 

[scubascobey]

Thought it might be helpful to share the "Basic Weight Guidelines" from PADI:

Exposure Suite Type: Start With:
3mm/1/16 in 1 pc wet suit (shorties) 1-4 lbs
5mm/3/16 in 2 pc wet suit 5% of body weight
7mm/1/4 in wet suit (hood & gloves) 10% of body weight + 3-5 lbs
Neoprene dry suit 10% of body weight + 7-10 lbs
Shell dry suit, light undergarment 10% of body weight + 3-5 lbs
Shell dry suit, heavy undergarment 10% of body weight + 7-14 lbs

SALT/FRESH Water Change
Body Weight: Add (going to salt) or Subtract (going to fresh):
100-125 lbs 4 lb
126-155 lbs 5 lb
156-186 lbs 6 lb
187-217 lbs 7 lb

CYLINDER adjustment
With aluminum 80, add 5 lbs. With other cylinders, there is no need to add weight.

 

[limeyx]

This is the finesse of drysuit diving. Using BOTH BC and DS.

Wings = gross buoyancy management
Drysuit = "not squeezed" puts you darn close to neutral
Lungs = fine tuning

Not really. Think of it this way.
Imagine I could fill my drysuit with some magical substance like air that removed the squeeze and kept me warm, but had no buoyancy increase whatsoever.
To me, this would be a preferable solution, resulting in a much easier ascent (of course this magic substance does not expand on ascending either



I would then be using only the BC -- the fact that the air in the suit currently adds to the buoyancy is just a side-effect that "air does that" nothing to do with air in the drysuit making you "neutral" or not -- you need to put air or argon in to remove the squeeze, and the fact that it give you a bit of lift is just a side-effect.

 

[Thalassamania]

Not really. Think of it this way....

I think that you and ICEGIRL (and I) are all saying basically the same thing in slightly different words.

 

[limeyx]

I think that you and ICEGIRL (and I) are all saying basically the same thing in slightly different words.

Possibly. I am simply saying that the ideal way for me is:

Suit: No need for air or argon. Undergarments are warm and prevent squeeze
BC: Basic buoyancy
Lungs: fine tuning

However, with todays equipment, we cannot get that as we have to prevent squeeze, so as a side-effect of that since air/argon inherently provide us some buoyancy, we are stuck with essentially an imperfect solution with two buoyancy devices, rather than having this as a "desired" state of affairs.

 

[Thalassamania]

Possibly. I am simply saying that the ideal way for me is:

Suit: No need for air or argon. Undergarments are warm and prevent squeeze
BC: Basic buoyancy
Lungs: fine tuning

However, with todays equipment, we cannot get that as we have to prevent squeeze, so as a side-effect of that since air/argon inherently provide us some buoyancy, we are stuck with essentially an imperfect solution with two buoyancy devices, rather than having this as a "desired" state of affairs.

Quite so. We played with some suits in the late 1980s that were supposed to be true "constant volume suits," they did not work very well.

 

[limeyx]

Quite so. We played with some suits in the late 1980s that were supposed to be true "constant volume suits," they did not work very well.

I can always hope though, right? It would be nice to be able to ditch the argon bottle and not have to vent the suit on ascent...

 

[Thalassamania]

I use a Sitek auto-dump valve. If works great for me. I start just this side of shrinkwrapped. I close it all the way, give my suit a little shot then open it till it starts to bubble, I close maybe an 1/8 of a turn. On descent I give my suit a shot every now and again whenever I'm feeling to tightly wrapped.

I've dumped my bc and lungs enough to start my descent.

I hold the oral inflator down (deeper) and open and I raise it in the water column until it just starts to bubble.

As I descend I give my BC a shot of air every now and again to slow my descent, but I continue to hold the oral inflator open (some designs you need to close the oral inflator or all the gas just runs out there). If I'm too heavy I lower (deeper) the oral inflator, too light I raise it (shallower).

Once at depth I rarely have to mess with my suit, the valve's done it's job and my BC is just about dead on ... maybe a tiny tweak and I'm on my way.

Coming up I reverse the process. My suit stays just about where it should and I control my ascent speed by holding my oral inflator open and lowering it to speed up or raising it to slow down (like an elevator, only backwards).

Try it, you'll like it.

 

[limeyx]

I use a Sitek auto-dump valve. If works great for me. I start just this side of shrinkwrapped. I close it all the way, give my suit a little shot then open it till it starts to bubble, I close maybe an 1/8 of a turn. On descent I give my suit a shot every now and again whenever I'm feeling to tightly wrapped.
...
I hold the oral inflator down (deeper) and open and I raise it in the water column until it just starts to bubble.
...
Try it, you'll like it.

I am not sure what you mean by "oral inflator"
I have a Si-tech exhaust valve, and an Apeks inflator (on suit) which is hooked via an LP hose to an argon bottle (or back gas)

On descent, I usually add to the suit first to relieve squeeze but regulate descent with BC.

Exhaust valve is left 100% open all the time.

On ascent, the gas starts to expand in the suit. Since I'm horizontal ascending, I have to lean a bit so my left side is up (to let the gas migrate) and squeeze my left arm (like I am lifting a weight I guess) to exhaust the gas.

if I try to just let the gas escape on its own, it exhausts way too slowly and I feel like the michelin man. I hate any significant amount of gas in the suit on ascent.

i dont seem to have an oral inflator for my suit (but I dont think that affects things much -- it's the venting that is irritating)