Vest-style BCD better for buoyancy???

[stuartv]

I’m just about to make the switch to a BP/W (or possibly other Back Inflate BCD), but now I’m thinking that a traditional vest BCD is probably better for buoyancy.

You say you're talking about buoyancy...

Let’s agree that much of the time, you want to be in a true horizontal position. When in that position, any air in a vest-style BCD will be in the back part of the BCD anyway (unless the BCD is close to fully inflated) and will help to keep you horizontal, just as in a BP/W or back inflate BCD.

But when I’m diving a wall or pinnacle, I often want to be facing the view, either by swimming somewhat on my side (rather than flat towards the bottom) or floating along the wall at a heads up angle, rather than just keeping my head turned. Likewise, if I’m scanning around for things in the blue, it seems more comfortable to be either be sidewise or more vertical, rather than doing everything with my neck.

With a vest-style BCD, when you roll sidewise, some of the air goes to your top side, helping to keep that position. A BP/W would tend to want to roll you back to horizontal position. When angled up, a Vest style BCD may give you a little air on your front to diminish the effect of being somewhat pivoted back down by air that was just on your back.

There are also times when you want to be even more vertical, such as while waiting for a boat on a choppy surface or when going upside down to look under a low ledge with even less chance of churning the bottom, For these, a vest will make things a little easier than resisting the pivot from having all the air on your back.

I’m fully onboard with the other benefits of a BP/W, such as the ability to mix/match or replace individual components, switch out wing sizes, the use of a steel plate as a substitute for other weighting (when travelling with it isn’t an issue), reduced amounts of materials in the shell, etc.

I’ve just been thinking that a) the ability for some air to move towards your sides and front when you have chosen not be horizontal is actually an advantage of the old-fashioned BCD and not a disadvantage and b) that (assuming weighting is similar) when you are horizontal, an old-fashioned BCD’s buoyancy isn’t making it harder to stay horizontal.

Quite happy to be convinced otherwise.

... but then all you talk about is trim.

None of them are better or worse for buoyancy - EXCEPT that different BCDs (a term which encompasses BP/Ws) are easier/harder to vent gas from. A BCD with an air cell that is way bigger than what is needed can make it harder to get all the air out of when you, for example, are at the end of a dive, with a nearly empty tank, and want to be able to hold your safety stop. With a BCD like that, people will often end up over-weighted because they think they need it, because they don't realize they are simply not getting all the air out of their BCD.

BP/W are *usually* better/easier for getting all the air out, simply because they are typically a smaller volume air cell and because the design lends itself to not trapping air inside.

All that said, all your discussion of holding different orientations is nothing to do with buoyancy. It is trim. Trim *is* your orientation in the water.

Is a jacket better for maintaining "non-standard" trim positions, e.g. being on your side? TBH, I don't know. I suppose it could be. For being vertical - head up or head down - a BP/W works perfectly fine when under water. When on the surface, I would say yes, a jacket will make it easier to be vertical with your head high out of the water. However, a BP/W works just fine for many, many people (including myself) for floating on the surface and keeping one's head up out of the water. Maybe not as high out of the water as with a jacket, but is that really especially useful?

For laying on your side, I don't have any trouble holding that when diving a BP/W with a single tank. When I dive double steels, laying my side does require a bit of finning in kind of a corkscrew motion to keep my tanks from just rolling me on my back. But, it doesn't bother me in the least.

In the end, the many advantages of a BP/W outweigh (for ME, anyway) the possible advantages that a jacket offers in holding my head higher out of the water at the surface and (maybe) being easier to stay in a side-laying trim position.

 

[Badger7]

When I dive double steels, laying my side does require a bit of finning in kind of a corkscrew motion to keep my tanks from just rolling me on my back. But, it doesn't bother me in the least.

and to restate the (hopefully) obvious, you wouldn't be diving twinset with a BCD anyway, so holding horizontal trim sideways in a BCD versus BPW with a twinset configuration isn't really a comparison

From the perspective of a guy who's dove traditional BCDs for a couple decades, and has recently converted over to an aluminum backplate for saltwater travel, and a steel backplate for local drysuit diving - zero regrets and zero compromise. Other than when I'm waiting for a boat pickup instead of bobbing like a cork in a BCD, I'm leaned back in a lazyboy position in a BPW if its going to be more than a few minutes. Underwater, its SOOOOO much easier and less energy to fin when you're in horizontal trim, not kicking yourself up or down the water column. Weighted properly, a BPW is so much easier to hold horizontal trim than a BCD.

Rent or borrow a backplate, get properly weighted in a pool and try it out, chances are you'll love it.

 

[stuartv]

and to restate the (hopefully) obvious, you wouldn't be diving twinset with a BCD anyway, so holding horizontal trim sideways in a BCD versus BPW with a twinset configuration isn't really a comparison

Fair point.

From the perspective of a guy who's dove traditional BCDs for a couple decades, and has recently converted over to an aluminum backplate for saltwater travel, and a steel backplate for local drysuit diving - zero regrets and zero compromise. Other than when I'm waiting for a boat pickup instead of bobbing like a cork in a BCD, I'm leaned back in a lazyboy position in a BPW if its going to be more than a few minutes. Underwater, its SOOOOO much easier and less energy to fin when you're in horizontal trim, not kicking yourself up or down the water column. Weighted properly, a BPW is so much easier to hold horizontal trim than a BCD.

If you setup a jacket BCD properly, it is also no effort to hold horizontal trim. I think the main reason you rarely actually see that is because you usually only see jacket BCDs being used by relatively new divers, who have not set them up properly and are also not especially skilled in staying in horizontal trim.

Don't take that the wrong way. I am not advocating in favor of using jacket BCDs. I'm just saying that we shouldn't knock them for reasons that are not actually valid. There are plenty of valid reasons to knock them.

 

[Blackcrusader]

Weighted properly, a BPW is so much easier to hold horizontal trim than a BCD.

Rent or borrow a backplate, get properly weighted in a pool and try it out, chances are you'll love it.

A properly setup BCD there are no issues with being horizontal or in any other position. I see many vacation divers who rent BSC's that do not have inserts or weight pockets at the shoulders. See the picture I posted on page 1 you can see I have no issues with being horizontal in my BCD due to being weighted properly.

The Korean lass I was diving with also properly weighted.

 

[happy-diver]

Weighted properly, a BPW is so much easier to hold horizontal trim than a BCD.

Tell me about it

Here I is going to where I want to go the way I want to go there with perfect trim and buoyancy

Like an aeroplane

 

[Imla]

To add a different perspective. As a classic A shape female, the traditional Jacket BCD/Backinflate with a cummerbund had me LOWER in the water when floating vertical on the surface than I do with a BP/W.
The JacketBCD would without fail, ride up under my arms. No matter how hard I tried to cinch the cummerbund/straps.
When I switched to a BP/W with a crotch strap I ended up higher in the water, even with less air in the wing, just because I didn't sink through the BCD because of the mismatch between slim torso and wider hips.
I have never had issues adjusting trim/positioning with a BP/W. I have no issues being head up, head down, on my back, normal flat trim, or just plainly at an angle. I just think that diving and getting comfortable with YOUR gear, will get you where you want to be. For me, a jacket vest is horrible, and personally, I'll just stay topside with a frothy cold honeycoloured melted "icecream" than diving in a jacket vest.

 

[FreqFlier]

Or you have it in the wrong places

Ditto
It's more about proper weighting and proper weights distribution - very important for good a trim

mismatch between slim torso and wider hips

Exactly.

@amg - BP/W allows for less weights since it is a bit less (or much less with steel plate) buoyant than any style BCD. Other than that there is no major difference besides body shape issues as @Imla stated.

Personally I can be stable in any position - vertical, horizontal, on the back - with my Alu BP/W no issues

 

[johndiver999]

To add a different perspective. As a classic A shape female, the traditional Jacket BCD/Backinflate with a cummerbund had me LOWER in the water when floating vertical on the surface than I do with a BP/W.
The JacketBCD would without fail, ride up under my arms. No matter how hard I tried to cinch the cummerbund/straps.
When I switched to a BP/W with a crotch strap I ended up higher in the water, even with less air in the wing, just because I didn't sink through the BCD because of the mismatch between slim torso and wider hips.
I have never had issues adjusting trim/positioning with a BP/W. I have no issues being head up, head down, on my back, normal flat trim, or just plainly at an angle. I just think that diving and getting comfortable with YOUR gear, will get you where you want to be. For me, a jacket vest is horrible, and personally, I'll just stay topside with a frothy cold honeycoloured melted "icecream" than diving in a jacket vest.

This is so interesting to me. Why in the world would you not at least try a crotch strap on a bc, if that is the exact problem you are having? A $2 strap from an old life jacket will work fine for experimentation, if not full time use.

 

[Imla]

This is so interesting to me. Why in the world would you not at least try a crotch strap on a bc, if that is the exact problem you are having? A $2 strap from an old life jacket will work fine for experimentation, if not full time use.

Why would I want to try a crotchstrap on a bcd not made for a crotch strap?
Because the bcd I had did not have the option to add a crotch strap. Because I did not like the fit/form of the bcd. Because I had friends that let me try their BPW which I immediately liked. Because of the crotchstrap. The stability. The trim. The lack of stuff and fluff all around. The durability.
I had already tried a number of bcds. Both backinflate west types, and traditional jacket wests.
So... In stead of you $2 solution. I got a 0$ solution when I got to borrow my friends wing to test. I would have had to buy a new bcd anyways.
My current BPW is going on 13 years, and close to 750 dives without any real signs of wear/tear.

 

[Learner Diver]

It's really a decision which you need to make for safety and comfort. Personally, I would want both. But I believe you can change out the wing on the backplate.