Want BCD that gives me same buoyancy at any pitch angle

[KevinNM]

So you have concluded that bondage wings suck. What are you planning on doing about it?

 

[Eric Sedletzky]

The only thing that will make air compress underwater is depth with increased pressure pushing in ON ALL sides of a soft bag.
If you have a flexible soft bag, balloon, plastic bag, lift bag, safety sausage, whatever, it will have a constant volume of air at a given depth no matter how you squeeze it. The only way to overcome this would be to wind up the whole bladder with cord thus creating a rigid container not allowing the air to expand in any direction upon ascent. Or if the bag reaches it's flexible limit and the material is strong enough to withstand the increasing pressure of expanding air and has no way to vent. But if you leave an open soft end somewhere that's where the air will go.
A least six people have tried to explain this to you. If you don't understand this basic principle then I don't know what further to tell you. You didn't school anybody dude, that's just basic physics.
Happy diving.

 

[DaleC]

Anyhow it sounds like a wing is something to try. Thanks to all the helpful people.

Ugh... A wing will not help, you already have one. That is a large horseshoe style wing. What may help is a wing with less lift and no bungee's. Or just not using it for primary buoyancy control.
Going back to what I said about orientation. Imagine the buoyancy difference if you are heads up compared to heads down. That bag is huge down near the butt. Look at the wing this person is using in comparison.

 

[runez]

One thing I've learnt reading these kind of threads on SB is - if you find one guy arguing against everyone else, chances are the one guy is wrong.

 

[Kharon]

If you cant understand that the loose end expands and displaces more water because there is no force holding it back like the other side, then you should get out your junior high school books.

Or admit that you were schooled here in Advanced Scuba Discussion.

The only person getting schooled is you - except you seem incapable of learning. Perhaps you should listen & think reather than simply think up what your next incorrect statement will be. Or get out your jr. high chem or physics books, assuming you progressed that far.

I trust the guys that came up with the gas laws. Air at a specific pressure in an elastic container will have a specific volume that will not change unless pressure is added or removed. It matters not one whit what the shape of that elastic container might be.

This was covered extremely well in my Physical Chemistry course as an undergraduate. It was also covered, although with a bit less mathematical rigueur, in my SDI Open Water class.

 

[The Chairman]

One thing I've learnt reading these kind of threads on SB is - if you find one guy arguing against everyone else, chances are the one guy is wrong.

Like when everyone said I couldn't teach students off of their knees for the entire class? Often, when you follow the masses, the 'm' is silent.

There are more ways to dive than agencies out there. There are many different theories on how buoyancy & trim work. It doesn't matter if we all agree as long as we are approximating the desired outcome with our favorite theory. Most of the people who don't like BWOD (Bungeed Wings of Death) have never dove one. They are full of misconceptions and inferences that never seem to jive with my experiences with them. Many people want to jump on the BP&Wing bandwagon. There are lots of reasons, and many are as kookie as the BWOD detractors. It's hard to accept that if someone doesn't dive like you then they are not going to become a statistic underwater, but the sooner you get there, the friendlier we can be about our differences.

Think about it. If you are not letting air in or out of your BC as you reorient yourself, then that can't be much of a change. The only large variance that I can visualize is the diver's lungs. The vertical swing between the reg down and the reg up is anywhere from 6 to 18 inches. That means the ambient pressure swing is probably about 6 to 18 inches of water. That amount of pressure will cause your lungs to be either over or under inflated (depending how you look at it) and easily accounts for the buoyancy variation. Ergo, if the lungs are causing the instability, then changing the BCD will likely have little effect on the issue. Anticipating the pressure swing and controlling your breathing is the obvious choice. At least it is for me.

In addition, even of the bladder were the issue, like on descent. Adjusting your lung volume on the fly is an easy way to compensate for it. Unless I have on a lot of exposure protection or am diving relatively deep, I seldom adjust the air in my bladder mostly because I am close to neutral without any air in my bladder as it is. Not overweighting yourself makes diving easier all the way around.

 

[DaleC]

Pete, while I think the shape of BC can effect performance in various orientations your point about becoming more neutrally buoyant is spot on. That is the most effective strategy the OP could employ to solve their issue.

Once you are close to neutrally buoyant, the amount of air you need to add to a BC is minimal, so you can look at using a smaller one next time you buy. When you look at a smaller one you can also look at design considerations such as jacket, donut, horseshoe. But the first step is buoyancy.

I also don't get hung up on bungee's. I understand the theory used against them, that if there is a failure the bungees will squeeze air out of a BC where one might otherwise be able to trap and use it for lift. But for performance they will do as well as any other. I also don't subscribe to the craziness over jacket BC's. Truth is, they work just fine. I like my BP/W for other reasons such as modularity and simplicity but not really for performance.

 

[TSandM]

It's not clear to me exactly what the OP wants to be able to do. If you want a rig that will balance perfectly in all attitudes, that's hard; you have to have the center of gravity directly above or below the center of lift in all orientations. Most setups won't do that -- if you are perfectly balanced in a horizontal position, you may not be balanced in a vertical one. But if you are balanced in a horizontal, prone position, you ought to be balanced in a horizontal, supine position. However, I have found that isn't necessarily so -- I had to work quite hard to figure out how to adjust my breathing when I flipped upside-down and lay on my back. The amount of gas in my wing didn't change, but maybe it was a little bit lower in the water column, now being BENEATH the tank. Or maybe I just find it difficult to take the same breath when upside-down. But whatever it was, I tended to sink as soon as I flipped over.

So if THAT is the OP's issue, I think more practice might solve the problem, because it did for me. Of course, being precisely weighted and having as little air in the BC as possible helps a lot, too.

 

[The Chairman]

Pete, while I think the shape of BC can effect performance in various orientations your point about becoming more neutrally buoyant is spot on. That is the most effective strategy the OP could employ to solve their issue.

Thanks for your kind words!

Once you are close to neutrally buoyant, the amount of air you need to add to a BC is minimal, so you can look at using a smaller one next time you buy. When you look at a smaller one you can also look at design considerations such as jacket, donut, horseshoe. But the first step is buoyancy.

I agree with the first part, but not the second. The search for the absolutely smallest BC is a fool's errand and can lead to not having enough lift when you need it most. No matter how big your bladder, you can still get your Scuba unit balanced to the point so you don't need much air in it. You might get some tacoing if the wing is really over sized, but there are ways to compensate for that, including bungees. The danger of bondage wings lie mostly in a few people's overactive imagination and not in reality.

I had to work quite hard to figure out how to adjust my breathing when I flipped upside-down and lay on my back.

It's all about the breathing, ain't it? Throwing gear at a training issue, even if it's the revered BP&Wing, is frustrating when it doesn't work out. FWIW, keeping the COG is easier if there's not much of a bubble shift. The closer you are to zero air in your BC and even your drysuit will enable that. The first is easy but doing that to the second is counter productive. Air=warmth.

 

[DaleC]

I was suggesting smaller as in comparison to the 70lb lift of his current model. There is no way any recreational diver should ever need that much. It makes for a very floppy bag with lots of bubble travel troubles, especially in a closed horseshoe design which it looks like, wherein you can trap all the bubble on one side. While I am luke warm on the bungee hysteria I don't see why one would choose an excessively large bag and then compensate with a modification (bungee) when you could just pick moderate size at the start. That's not a criticism of the OP, we all make unknowing purchases when we start. My suggestions are only meant to give some ideas to consider during the next purchasing cycle.

For the average joe I would look in the 30-40cuft range.