BP/W - what's the go with air movement in the wing?

[gxtoast]

This is not a question I have seen asked or answered on these forums before.

One of the things I experienced recently, using a rented jacket BCD, was the movement of air from "top" to "bottom" or end to end (depending on my position). This was disruptive and somehow the movement also caused buoyancy problems, in that it was difficult to stay neutral at times. Odd, considering the air was just moving around.

Anyway, looking at the wings used on backplates and harnesses, it seems that air movement might also be a problem for these devices in that they also have a single bladder. Air must move around the bladder when it is only partially inflated.

Has anyone had any experience with this issue, or is it something that does happen but is not disruptive.

Cheers,
Nick

 

[a22shady]

I only used a Jacket on my 1st Pool Session. Then bought my BP/w Halcyon Eclipse. I can't say I noticed Air Movement. I know it was little more difficult with the jacket vs Bp/w and I have been using it for about a year now and can't say I have ever had an issue with Air movement. I am sure it has moved when shifting body Position as that is the nature of Air. Why we elevate the rear when dmping air from the dump valve. But as of yet have not had a problem

 

[Bubbletrubble]

@gxtoast: Your observation is an interesting one: air changes position inside the bladder which sometimes makes it "difficult to stay neutral." If you aren't adding/subtracting gas to the wing, then your wing is not the cause of your buoyancy issues. Other factors that affect buoyancy include: the gas inside your lungs, compression of your wetsuit, and loss of gas from your tank.

Air is going to move around inside the BCD bladder. That's just how it is.
The bladder will have varying shapes depending on the design of the BCD. The important thing is that air can easily be dumped from the BCD.

Don't rush out to buy an expensive BCD or BP/W to address this issue. I suspect that with more experience this will become a non-issue for you (regardless of the style of BCD that you use). It will just take time and practice. Good luck and have fun out there!

 

[Tortuga68]

Has anyone had any experience with this issue, or is it something that does happen but is not disruptive

It's more on a single plane so not so disruptive when in horizontal trim, which is much easier to maintain with a BPW than a jacket

 

[rcs9250]

Also, do a good buoyancy check to make sure you are not overweighted, resulting in a large bubble in your bladder. New divers often forget to do a good check after being certified. Don't forget, with any change in your dive kit, it can affect your weighting. Sometimes it's a miniscule change but sometimes it's not.
As you are probably aware , you wouldn't use the same weighting for a dry suit or a 3mm wet suit.
Really, the best way to determine your weighting is at 15' with about 500 psi in your cylinder. Start your dive anticipating being able to easily remove 1,2 or 4 lbs while on your safety stop. Hand it to your buddy. Then let the appropriate amount of air out of your bladder to become neutral. If there is still air in the bladder, hand off some more weight. It may take one or two dives to get it just right. Once you learn it record it in your log book for that exact combination for future reference.
Once you figure out the proper weight don't forget to then figure out the trimming so you are horizontal in the water.
Remember, a steel 80 and an aluminum 80 will vary the amount of weighting required. Trim will be affected as well.
I dive several combinations and have a record of each.

 

[Wayne at DiveSeekers]

Divers have more "Control" in the water with a BP & Harness than any other set up on the market. First off the BP keeps you more horizontal and in trim. Secondly, the wing mounted behind you helps as well. IMO, the best wing to go with is a donut style oppose to a "U" shape. I personally believe that you have a faster response time when venting these wings and you have equal distribution of air both side to side and top to bottom. I am a dealer for a couple of different manufacturers and I have found the Halcyon Eclipse wings give you the best overall "Control" in the water. With this wing, you won't have any trapped air and no delay in response to buoyancy that you have with a Jacket style or "U" shaped wing.

Here is the system that I am referring to.
Halcyon Eclipse System HES *Buy Halcyon at DIVESEEKERS.com 888-SCUBA-47

It does tend to be a little more pricey but when you factor in features & performance of the system, it's well worth the money.

 

[TSandM]

Air moves around in wings, too. Sometimes you do it on purpose -- for example, if you look at technical divers carrying one or more extra tanks on the left, they use extra gas in the left side of the wing to balance that gear.

Sometimes it happens inadvertently. If you use your butt dump a lot, you're dumping out of the left side of the wing, and if you are perfectly horizontal or a little head down, the air can't move around and equalize between the two sides. You can end up diving on your side that way (don't ask me how I know this). The solution is simply to go a little head up for a moment, and allow the air to move around until it's evenly distributed.

The only way I can imagine that type of air movement affecting neutral buoyancy is if, for example, you tilted head down by having your feet move UP -- then the bottom of the wing would be higher than it was before, and the gas would expand a little and you'd get a little positive. And, of course, if you're in a drysuit, that type of movement is magnified by the expansion of the gas in the suit as well.

 

[rstofer]

Consider a cold water wetsuit diver (7mm) with an HP 100. The suit probably provides 25# of buoyancy at the surface and loses about half by 30'. At the start of the dive, the tank is 8# heavier than at the end. So, at 30', the wing has to provide 12.5# + 8# or about 20# of lift.

That 30# wing is pretty full even at such a shallow depth. Later in the dive, when the tank is depleted, the wing is still providing 12# of lift; it's still between 1/3 and 1/2 full.

I guess the point it that for a proper sized wing, there will always be enough air to help it keep shape and having the bubble move from side to side isn't such a big deal. But throw an oversized 40# wing into the mix and now one side can hold the entire bubble.

What about the T-shirt diver? Well, they need a lot smaller wing!

BTW, the Deep Sea Supply rig is a lot less expensive than the Halcyon and although I use the LCD-30 U shaped wing, there is a torus wing available in 26# or 35#. I think I would opt for the 35# because 26# might be marginal at 100' where the wetsuit has given up most of its buoyancy.

Richard

 

[Web Monkey]

This is not a question I have seen asked or answered on these forums before.

One of the things I experienced recently, using a rented jacket BCD, was the movement of air from "top" to "bottom" or end to end (depending on my position). This was disruptive and somehow the movement also caused buoyancy problems, in that it was difficult to stay neutral at times. Odd, considering the air was just moving around.

I'd be willing to bet that you're overweighted. With a single 80 (I'm assuming because you said "rental"), you shouldn't need very much air in your BC at all. If you notice it moving around, you probably have too much air in your BC, which is caused by too much weight on your weightbelt.

If you fix the weight problem, the "air moving" problem should vanish.

Anyway, looking at the wings used on backplates and harnesses, it seems that air movement might also be a problem for these devices in that they also have a single bladder. Air must move around the bladder when it is only partially inflated.

Both BC styles are just bags that can hold air and both will behave about the same, given the same conditions.

Terry

 

[Blue Sparkle]

I am a dealer for a couple of different manufacturers and I have found the Halcyon Eclipse wings give you the best overall "Control" in the water. With this wing, you won't have any trapped air and no delay in response to buoyancy that you have with a Jacket style or "U" shaped wing.

Would you mind elaborating on this a bit? I can't tell for sure if you are saying that the BP/W style of BC gives the best control, or if you are saying that of the BP/W's, the Halcyon wing is superior to others (in your experience).

Thanks ahead for clarifying,

B.