minimalist back inflate BC?

[jhelmuth]

Apology not required (no offense taken since I am amoung those who use little weight and do not need much lift). I just wanted to be clear that I am NOT for larger bladders. If anyone goes back to look at my initial response, I am really questioning the need for so much weight. I was fortunate enough to have listened to many who convinced me that I needed to minimize my weight to really get neutral in the water AND be in control. They were right and I'm an advocate for sheding lead. For my typical diving (warm waters and very litlle neoprene), I have very little weight requirement (I'm 6'1" and 212 lbs). If raposarose (6'2" and 185 lbs) really requires 32 lbs of lead, then I think he needs to seriously consider a BCD with a lift capacity of at least 40 lbs (but as small a profile as possible in terms of the "hole" created by it, to reduce the drag). I agree with your comment on having a minimally inflated bladder move air and potentially creating trim problems. The optimal is to have a bladder/wing which minimizes the "hole" size created in the water - low profile if you will (to reduce drag) - and to have it inflated enough that air movement does not create a trim issue. I don't really know for sure where that is, but I suspect that it is somewhere around a 1/2 inflated bladder. I can say that because that is my experience. For myself, I like having the extra lfit capacity for other reasons. These include: being able to add neoprene for warmth if needed; being able to help a fellow diver if they loose a weight belt (yes - it has happened and I did not mind getting it for them - but I did like having the extra lift so I could easily swim the belt up (had 18 lbs on it); just in case I do have to rescue a fellow diver who has lost their BCD lift at any significan depth (losing their weight belt here is a last ditch, life threatining only option, as they will now shoot us both to the surface as we ascend); and lastly - just incase I put on some fat (I'm getting older and lazier with age).

Anyway, I enjoyed our discussion and am still open-minded to reasons for not having excess lift (IE - why I should select a blader that requires me to infalte it to much more than half its capacity). I do agree that one must consider the air movement as it affects trim - and I do think that is a reasonable and highly desired trait worthy of careful consideration. So in the end... not so large that it affect your ability to maintain good trim in the water, but not close to maximum capacity either.

 

[jplacson]

Well, with regards to trim... I think if needs be, it's much better to reach your BCs full capacity rather than having it half inflated since all BC wings were 'tested' at full inflation. Since at full inflation, the bladder holds it's 'hydrodynamic' shape more than at half inflation... you get a smaller profile when deflated, and if needed, you use the bladders maximum streamlined design efficiency when fully inflated. You can experiment with this in a pool... half inflate your BC then drag it across the water... you'll notice that the front part (the part behind your head) flops around and takes the shape of a small fabric scoop. At full inflation, the bladder becomes easier to drag through the water since the water just slides across the sides and the front "hull" of the bladder doesn't change shape.

But, IMO, drag isn't that big an issue since we're not in a race... but this is just my opinion.

 

[DA Aquamaster]

I agree totally with the need to weight yourself properly and would suggest that many if not most divers are overweighted.

I would further suggest that many instructors overweight students as as faster and more convenient way get them under than to address the real problems.

But I feel this is a separate issue from the the argument for bladder size. I dive cold water with either a dry suit with heavy underwear or a 7mm semi-dry. With twin steel 72's, redundant regs and a stainless steel back plate I need 12 lbs in the weight pockets to be neutral at 15' at the end of the dive with 200-300 psi in both tanks. I am not overweighted by any means.

However on the surface a 75 lb wing is nice in order to get me comfortably above water in waves and chop. Without me and my bouyant exposure suit in it, my setup still floats on the surface with a comfortable margin of reserve lift. With full tanks, the back plate, tank bands, integrated weights and a pair of regs, the lift requirement just to keep it on the surface is probably close to 40 lbs so a 45 lb wing would not leave much margin of additional lift.

This extra lift also allows me to assist an overweighted or underlifted buddy under water as well as at the surface. I have not encountered any problems with the air required to maintain bouyancy at depth shifting in the extra space available in the 75 lb wing. In my opinion, this potential problem is more an issue of poor wing design and/or the unsuitability of the specific wing design to the application (singles, doubles, etc,) than an issue of excessive lift capacity.

It does create the potential to develop a greater excess of lift in an out of control ascent which could exaggerate the problem. But then an out of control ascent is not a problem for a competent diver even with a stuck inflator.

My spouse had a tropical BC for a while with 28 lbs of lift and even with just a single 80, it was just barely adequate to keep her chin above water with the expousure suit and weight requirements inherent in cold water diving. Add a wave or two and she was uncomfortable in the water and having to fin to avoid taking water in the face.

Her current BC offers 45 lbs of lift, allows her to relax at the surface before and after the dive and is in my opinion the minimum lift capacity that should be used in cold water. 25-30 lbs of lift capacity is fine in the tropics with 2-3mm suit, an AL 80 and maybe 6 lbs of weight, but it won't cut it in the rest of the world.

 

[jplacson]

DA, 36-45# in cold water is fine. The amount of lift needed changes depending on exposure suit and weight carried anyway.

As for floating on the surface, that's fine as well. I do prefer using a separate floation device like a CC lift bag or marker balloon since a fully inflated wing does have tendencies to plant you face down... I just inflate my marker sausage (40# extra), then drape my amrs over it... this way, I have more lift in front of me, while making me more visible to the dive boat. But that's just me.

Most divers I dive with would rather just have a lot of lift in their BCs at the surface to rest with... I prefer the absolute minimum for diving, then carry a redundany lift device... besides, I feel that marker sausages should be a requirement... more so for novice divers who may drift away from the group.

If they could only make elastic bladders (that offer the same puncture resistance as Cordura)...trim, drag, and lift problems would all be solved since the bladder would shrink and vanish with no air in it, and you could have a whole lot of lift this way... imagine having a TRUE wing for 'all kinds of diving' ... maybe if they invented some kind elastic Kevlar or Cordura?

 

[paulwlee]

IMHO, using yourself as a liftbag is a very dangerous practice. In an emergency, I guess using the human liftbag approach to help a buddy could be an option, but I would be very reluctant to become more than 10lbs positive at depth to do so, as then I will be unlikely to stop myself in the event I lose my hold. With the original poster, with 31lbs of weight, he will be negative by 25lbs at most at the beginning of the dive at 100ft. Subtract the 10lbs I'm helping, and we should be able to swim up the remaining 15lbs together pretty easily.

At any rate, a person should be weighted such that in a catastrophic BC failure he can ditch a part of his weight to be able to swim up.

For the above reasons, I still believe the 36lb bladder of the Balance (it's actually 40lbs if he ends up with size large) is more than adequate for his needs.

To add some more perspective, most people who dive single tanks with backplate and wings in my area dive with the 36lb wing. Some people even dive with the 27lb wing. The weight requirements around here are from the mid 20's to the low 30's, since we need either 7mm farmer johns or drysuits.
Also, all rental BC's at my LDS are Oceanic Flex QLR's, and they have even less lift than the Balance. (30# for size M, 34# for size ML) Actually, most jacket style BC's have less lift than the Balance, including the Oceanic Probe, Seaquest Pro QD+, etc. The only BC's that have more lift than the Balance are some higher end back inflates and the so-called 'tech' back inflate BC's, and that's because with double 104's and two AL80 stage bottles for example, the weight of your gas alone will add 27lbs at the beginning of the dive.

 

[raposarose]

That's a lot to consider that you have all brought up here.

I am not sure that the dive shops will let me dive these particular BCs before purchasing but I'll look around to see if I can find them to test first.

I don't think that 31 lbs is unheard of for cold water diving. Especially considering that the suit has more rubber than the jacket/farmer john suits. It is a warm suit and isn't bulky because it is a custom fit though. I can go 30 but it takes a little more effort to get down -- it is workable though.

It may be the case that the large Balance fits me. In that case it might work because of the greater lift capacity . I have tried on the Balance and Knighthawk on in person but I have yet to try the Transpac or BP. The Knighthawk felt better in the store but from the opinions I have gotten is seems that under water the Balance has more votes. Since people feel so strongly about the BP/wings I feel I owe it to myself to at least try it. There is a DIR shop nearby that I imagine must rent those.

So, I am glad to have learned more issues I should consider in making this purchase. At least I have eliminated the Escape from my list.

Thanks all,
Raposa

 

[raposarose]

I had a chance to try a Halcyon BP/Wings set-up this weekend. I suppose it is not too hardcore for a beginner to use. I felt very stable under the water and it was nice to get that 6 lbs off of my weight belt. Also, though just a touch of lumbar paddng would be nice it was not really uncomfortable on land. I also felt very comfortable on the surface swim. I was not pushed forward at all and could remain upright as easily as in a jacket BC. I swam out on my back and it actually felt easier to move on the surface. Nothing you don't know I suppose... I did not feel any revolutionary new amount of control or anything, but on the other hand I had no trouble at all with maintaining proper (horizontal) positioning.

I still would like to test out the Transpac II and the Balance just for the sake of comparison.

Best,
Raposa

 

[Dyno Bill]

I am 6'2", 185. I dive an old Dacor Rig with Body Glove 2 piece 7 mil wet suit in So Cal. I wear 16 lbs to dive deep and 18 lbs to dive the shallows using a lps 95. I dont dive aluminum any more due to the boyancy issues. I have never used a dry suit so I'm not familiar with proper weighting with one. I dont see where 30 lbs is a proper weight for a diver in a wet suit, thats a bunch to haul back up if you need to.
Bill

 

[Gator Diver]

raposarose --- the Halcyon setup is a good one, I have
tried it myself and found the same things that you
did. I have also tried the Balance and it definitely
takes more time to get your proper trim and buoyancy.
In the end I went with the Balance, but I can
see myself with a bp/wing setup in the near future

 

[jplacson]

raposarose, there's no such thing as too hardcore dive equipment.

you can get the MC storage pack if you need extra padding. if you still want more padding than that, you can stuff your marker balloon inside it.