Drysuit vs BCD bouyancy control

[cameron]

"Are you trying to tell me that you can get all that air out of a drysuit if needed faster than you can get it out of a bc bladder?"

For what reason would you want to get all the air out of you BC/Drysuit in such a quick fashion?


"dynamic stability problems"

I have no problems with air moving all over. On descent, most of the air sits across the top of my back. I can maintain a hover, I can swim in any direction, I can turn in both directions, you know the usual stuff we do underwater. I don't shoot to the surface or have any problems venting gas from my shoulder dump.

I dive a 7mm drysuit, with lots of undies to stay warm. Due to compression of the suit I have to add a fair bit of gas to maintain bouyancy. I am not overweighted as I can sink at the begining and maintain safety stop at the end. I just don't dive with a BC. whats wrong with that.

What about the techy types who use the drysuit as backup bouyancy. If it is so dangerous, then why would anyone rely on it for redundancy. If its as dynamicaly whatever, then I imagine it would be hard to keep a 20ft stop with only the drysuit.

You can also dive without BC while diving wet. Heavens no!! Try it in a pool. In a 3mm suit and a little weight, you can toitally control your bouyancy with your lungs. Blasphemy!! The vintage gear guys will back me up!!

The agencys arn't always right.

 

[Diver0001]

Are you trying to tell me that you can get all that air out of a drysuit if needed faster than you can get it out of a bc bladder?

Under what circumstances should this be a requirement? A drysuit can purge as fast as air goes in. Is there a compelling reason why that isn't fast enough?

Go back to basic open water - what did you learn about air, volume, and pressure. Boyles - remember.

These laws apply in equal measure no matter where you put your air. Why are you reminding us of this? What are we supposed to conclude from this point?

dynamic stability problems with not only the position of the air as it relates to the center of mass, but also Boyle's law at a multiplied factor.

Boyles law doesn't affect a drysuit any more than it affects a BCD. The point about dynamic (in)stability has to bee seen in context. I personally don't like to feel a bubble of air moving around in my suit but maybe another person doesn't mind the feeling. The issues (once again) are neutral buoyancy, good trim and comfort. Assuming you're skilled in diving dry then how it feels to have a bubble in your suit has to do with individual preference. Nobody who is skilled in drysuit diving is going to have a problem dealing with a little extra air in the DS.

If you don't see the potential danger in that, then I won't waste your time anymore.

Any potential danger in this would have to do with diver skill in the recreational context. Just last weekend I was diving with a friend of mine. We were playing around and I dove head down into a tube just wide enough to fit myself and my twinset (exit/entry on the bottom). I swam 1/2 way down it (about 5 meters down) and encountered another diver coming up. So I backed out of the tube (ascended 5 meters feet first because there was no room to turn around) and despite collecting a fair amount of air in my feet I never even came close to losing control. I reestablished neutral buoyancy upon exiting the tube. My buddy then entered feet first from the bottom and ascended the entire 10 metres up feet first and also reestabilished neutral buoyancy immediately upon exiting the tube. This fear about the feet up position in drysuit diving (which is what I read into a lot of these posts about the "dangers" of air in your suit) is, in my opinion quite unfounded if you have the skills. Having said that, I do keep most of my air in my bcd (so does my buddy) so I was able to dump air from my bcd as I was backing out of the tube. If you put all of your air in your suit you would probably make a mess of something like that and have to roll out of it once you had the room.

R..

 

[String]

Dynamic instability issues, a.k.a. air bubble moving should not be an issue if a diver isnt overweighted. Using either method for buoyancy control there is no reason to have a large moving bubble of air in the suit - that means too much air meaning too much weight.

 

[Daryl Morse]

I don't think it's fear. I think it's common sense.

Well said.

 

[mempilot]

For what reason would you want to get all the air out of you BC/Drysuit in such a quick fashion?

How long have you been diving and in what conditions? Do a search on this board and you find any number of incidents where the diver was forced into an un-commanded ascent due to upcurrents, malestation of their dive bouy, their buddy, from a lack of control, or from a number of other causes. If you don't see the possibility for needing to dump air from a bladder in a hurry, whether it be the bc or the drysuit, then you might want to consider retraining. Removing air from the bc is quick and easy. Getting the air mass to the dump valve on a ds isn't quite so simple in a lot of cases. Being properly weighted alleviates the need for a lot of gas in either, but you indicated in an ealier post that you don't see anything wrong with putting 'a lot' of gas in the suit.

I have no problems with air moving all over. On descent, most of the air sits across the top of my back. I can maintain a hover, I can swim in any direction, I can turn in both directions, you know the usual stuff we do underwater. I don't shoot to the surface or have any problems venting gas from my shoulder dump.

If you are putting so much gas in on the DESCENT that it pools over your back, your are way overweighted. On descent, you should be able to just put a blast of air in every so often to relieve the squeeze. If you need that much air on the descent to stay warm, then you are not wearing the proper undergarmets beneath your suit.

As for maintaining a hover, I have no doubts. That position would see the air mass spread over the the body in a proportionate fashion. Diving is not a 100% horizontal endeavor. If you never intend to be heads down or up while diving, then you might want to consider diving wet, because you will eventually need do something other than horiz, and with the amount of air you speak of, you are an accident waiting to happen.

As for venting gas from your shoulder dump: No problem. But, if you start out with an abnormally large amount of gas in the suit, and then get away on your ascent, you will not be able to vent fast enough to slow your ascent. Don't bluff on this. Maybe all your dives are shallow, but the deeper you go, the more dangerous it becomes to have that much gas in your suit.

I dive a 7mm drysuit, with lots of undies to stay warm. Due to compression of the suit I have to add a fair bit of gas to maintain bouyancy. I am not overweighted as I can sink at the begining and maintain safety stop at the end. I just don't dive with a BC. whats wrong with that.

How much gas is in your suit on your safety stop?

What about the techy types who use the drysuit as backup bouyancy. If it is so dangerous, then why would anyone rely on it for redundancy. If its as dynamicaly whatever, then I imagine it would be hard to keep a 20ft stop with only the drysuit.

I use my ds as a backup bouyancy device, but it is a backup only. The wing bladder is much more manageable for fine tuning bouyancy, especially when the need to be in all shorts of positions arising while wreck diving. The last place I want air when going head first down a stairwell is in my boots.

You can also dive without BC while diving wet. Heavens no!! Try it in a pool. In a 3mm suit and a little weight, you can toitally control your bouyancy with your lungs. Blasphemy!! The vintage gear guys will back me up!!

Where did this come from?

The agencys arn't always right.

I don't need an agency to understand physics.

 

[mempilot]

Under what circumstances should this be a requirement? A drysuit can purge as fast as air goes in. Is there a compelling reason why that isn't fast enough?

'A lot' of air already in the suit + air coming in > than amount of air that can be purged.

All you are doing is keeping up with the incoming air, not getting rid of the air that was already in the suit. In an uncontrolled ascent with too much air in the ds, this is a dangerous thing, and would require breaking the seal on the suit.

Also, the air needs to be accessible to the dump valve to get rid of it. If it's down in your legs and feet, it isn't going to come out the dump at all. Go and read all the threads on wing design and dump placement, especially the donut vs the horseshoe singles wing debate. The same rings true here.

These laws apply in equal measure no matter where you put your air. Why are you reminding us of this? What are we supposed to conclude from this point?

Again, if the air isn't accessible to the valve, then it isn't going to purge. Apply Boyle's to the air trapped down in your legs while you are ascending in an uncontrolled or uncommanded event. If it is trapped due to body position, then you are in for a ride. Keeping the air in a smaller package over the center of mass with direct access to a vent makes much more sense than packing it away far from a vent.

Boyles law doesn't affect a drysuit any more than it affects a BCD. The point about dynamic (in)stability has to bee seen in context. I personally don't like to feel a bubble of air moving around in my suit but maybe another person doesn't mind the feeling. The issues (once again) are neutral buoyancy, good trim and comfort. Assuming you're skilled in diving dry then how it feels to have a bubble in your suit has to do with individual preference. Nobody who is skilled in drysuit diving is going to have a problem dealing with a little extra air in the DS.

You may not feel the bubble, but read the other poster's comments about how much air they put in their ds. I'm not talking to you. I was talking to him. Please read the quotes along with the text to keep yourself from feeling picked on. A pool of air over his back on descent followed by a lot of air to stay warm. Either he is overstating his configuration to troll an argument, or he really is overweighted and therefore an accident waiting to happen. You referal to skill with a drysuit makes me chuckle, since one skilled in drysuit diving would understand the concepts behind undergarments, staying dry, and an air layer being the key to staying warm and not making yourself into the Michelin Man and then throwing weight on to stay down. If more gas layer were the answer, then our windows would have bigger gaps between the paynes. A thin layer of gas is all that is needed.

Any potential danger in this would have to do with diver skill in the recreational context. Just last weekend I was diving with a friend of mine. We were playing around and I dove head down into a tube just wide enough to fit myself and my twinset (exit/entry on the bottom). I swam 1/2 way down it (about 5 meters down) and encountered another diver coming up. So I backed out of the tube (ascended 5 meters feet first because there was no room to turn around) and despite collecting a fair amount of air in my feet I never even came close to losing control. I reestablished neutral buoyancy upon exiting the tube. My buddy then entered feet first from the bottom and ascended the entire 10 metres up feet first and also reestabilished neutral buoyancy immediately upon exiting the tube. This fear about the feet up position in drysuit diving (which is what I read into a lot of these posts about the "dangers" of air in your suit) is, in my opinion quite unfounded if you have the skills.

Were do you get that I have a fear of going feet up? I wreck dive every week. I go feet up on every dive, probably more than you do based on your example. Skill does have everything to do with diving a ds safely. Go back and read other's posts about the amount of air in their suits that they find acceptable. Feet up for them would be unsafe, if Murphy was hanging around for a good kick that day.

There are a lot of things that we could do in diving that would not nip us in the butt on any given day. We could load ourselves down with all kinds of crap, thinking we might need it. We could route our hoses this way and that. We could wear too much weight, because we can always put more air in to compensate. It's when things go wrong and now we have artificially enhanced the dangers due to lack of discipline and understanding.

Having said that, I do keep most of my air in my bcd (so does my buddy) so I was able to dump air from my bcd as I was backing out of the tube. If you put all of your air in your suit you would probably make a mess of something like that and have to roll out of it once you had the room. /QUOTE]

So, were you just trying to argue then or what? Because you just showed an example that contradicted your earlier argument.

.....


Look, divers can do whatever they want. 95% of the time they can get away with it. Skilled divers can cut that even further. I'm not ragging on you because you don't advocate pressurizing your suit to a 50lb lift bag like a previous poster.

 

[mempilot]

Dynamic instability issues, a.k.a. air bubble moving should not be an issue if a diver isnt overweighted. Using either method for buoyancy control there is no reason to have a large moving bubble of air in the suit - that means too much air meaning too much weight.

Very true.

 

[Diver0001]

I'm not talking to you.

I know that but there are a lot of people following this thread and some of them will be inexperienced drysuit divers. I'm just trying to keep some kind of focus on the big issues of drysuit diving (comfort, trim and buoyancy control). The example I gave about diving feet up was intended to address the biggest fear a lot of DS divers seem to have and to point out that with a little practice it's not a big deal. It wasn't directed at you (I assumed you're an expert drysuit diver given a quick look in your profile) it was directed at the message that you seemed to be communicating, which was that the feet up position is somehow dangerous. When I assist with DS lessons I have rank beginners in their first DS dive doing handstands, head down hovering and rolling out of feet first ascents in the pool so they can be taught how to control these situations instead of being told to fear it. Fearing something is giving in to the ignorance of not having learned it. I think you would agree.

I'm not trying to be argumentative, I'm just offering the lurkers a different point of view on the same issue. Accepting the fear isn't the way to go. If you (general you) fear the feet up position then you should make it a goal to acquire the skills to deal with it.

R..

 

[kazinvan]

'A lot' of air already in the suit + air coming in > than amount of air that can be purged.

All you are doing is keeping up with the incoming air, not getting rid of the air that was already in the suit. In an uncontrolled ascent with too much air in the ds, this is a dangerous thing, and would require breaking the seal on the suit.

You are assuming that one would be pressing the ds inflator while trying to dump the air. I don't see the logic here. If you are dumping air I don't think you would be trying to inflate the suit at the same time. So, the question is can the dump valve dump air faster than the rate of expansion during ascent? If you are at depth, say 100', then the rate of expansion is not that big and the valve can keep up just fine. Near the surface, things expand at a faster rate, and maybe (only maybe) the valve can't keep up, but near the surface it's likely less of an issue anyway. The ds can dump air relatively quickly (though my wing does dump it faster). I currently dive by only adding air to my suit, none in my bc for the whole dive. That may change, I'm still new to my bp/w.

One thing to note as well is if you are ascending too quickly and not venting air fast enough or often enough, if in a head-up position the suit will often "burp" and expel a lot of air via the neck seal. Had this happen a couple of times while I was getting the hang of diving with a ds.

 

[cameron]

"How long have you been diving and in what conditions?"

Well I don't want to get into a pissing contest about how much experience I have or you have. That would be futile. If you REALLY want to know I can PM you all my details...if it will make you feel better.

I dive a drysuit and no BC.
I have enought weight to descend. (not too much mind you)
As I descend, the drysuit compresses.
I add air to make up for the compression.
By the end of the dive I have a bubble of air on the top of my shoulders.
When I dive, I go upside down backwards and in and out. Whatever I need to do to see what I want.
I can always return to a good trim position.
As the tank gets lighter, I slightly role to the right and give myself a little hug to purge some air.
I complete the dive, with whatever stops are required.
When I get to the surface I can add some air and float if I need to.
I am alive and kicking.
I have been diving like this since I really learned to dive. ( not that long but enought time to know how to use a drysuit)

Don't be too convinced that your way is the only way.
If you don't want to dive like this....don't
But don't tell me it is unsafe or dangerous when you have never tried it.

let mwe know about that PM...ok