How much lift do I need in a BC?

h0lmes522 · Jun 30, 2011

So I'm building my own wing BC and need advice on the size. I'm only a recreational diver so all I need is a single tank bladder but I see wings with all different types of sizes: 30lbs, 32lbs, and 40lbs. I am 6'1" and 175lbs what would be an appropriate fit?

Tortuga68 · Jun 30, 2011

Height and weight has nothing to do with it really and is not a good way to judge

Try this: http://www.scubaboard.com/forums/bu...ems/158370-ultimate-wing-lift-calculator.html

Short answer: for AL80 tank rec diving, 30# is probably more than enough

jlevine · Jun 30, 2011

This is somewhat variable based on the individual. My BC for warm water (Zeagle Express) came with a 24lb bladder. It's fine for me for that situation.

CT Sean · Jun 30, 2011

It actually doesn't vary by individual at all. What you'll find if you read here is a wing needs to do two things:

a. Float your rig on the surface without you in it
b. Compensate for the loss of buoyancy due to exposure suit compression and gas loss

The body inside the BC is irrelevant

As Tortuga said though, the short answer is 30 is most likely plenty unless you are using tons of neoprene, high volume tanks and/or carrying all your weight on your BC rather than on a belt.

edit - I should say it doesn't vary by an individual's body type but DOES vary by individual's personal equipment configuration / needs

The Kraken · Jun 30, 2011

Enough so that if you have to take it off, it will be positively buoyant fully inflated with a full tank and all the gear and weight you'll have attached to it.

the K

fisheater · Jun 30, 2011

To be fair, the body inside the exposure suit does have an influence. Bigger body => more neoprene or undergarment => more buoyancy shift.

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vixtor · Jul 1, 2011

CT Sean:
b. Compensate for the loss of buoyancy due to exposure suit compression and gas loss

It doesn't compensate for gas loss (because if you have less gas, you are more buoyant, hence you don't need BC lift. It compensates for un-lost gas - the gas that you carry on your back. This means that for example, if your suit surface buoyancy is 10kg, and at 30 meters is only 3kg (theoretical figures, no practical relevance), and you have a 15 L steel tank with ~3.6kg of gas inside, then you need a BC that compensates for 7 kg plus 3.6kg of gas that you carry at the beginning, which means a 10.6kg of lift. After you breathe your gas, your tank becomes less heavy (let's say 1.2kg close to the end of the dive), which means that at that moment you only need 8.2kg of lift instead of the initial 10.6.

CT Sean · Jul 1, 2011

vixtor:
It doesn't compensate for gas loss (because if you have less gas, you are more buoyant, hence you don't need BC lift. It compensates for un-lost gas - the gas that you carry on your back. This means that for example, if your suit surface buoyancy is 10kg, and at 30 meters is only 3kg (theoretical figures, no practical relevance), and you have a 15 L steel tank with ~3.6kg of gas inside, then you need a BC that compensates for 7 kg plus 3.6kg of gas that you carry at the beginning, which means a 10.6kg of lift. After you breathe your gas, your tank becomes less heavy (let's say 1.2kg close to the end of the dive), which means that at that moment you only need 8.2kg of lift instead of the initial 10.6.

That's what I meant but I see how my comment easily implies a buoyancy loss due to gas loss. You are of course correct that the wing needs to compensate for the extra weight of gas that you start with.

scubafanatic · Jul 3, 2011

When in doubt, round upwards, there's less downside in having a bit more lift than needed, versus having less lift than needed.

eelnoraa · Jul 5, 2011

Tortuga68:
Height and weight has nothing to do with it really and is not a good way to judge

Try this: http://www.scubaboard.com/forums/bu...ems/158370-ultimate-wing-lift-calculator.html

Short answer: for AL80 tank rec diving, 30# is probably more than enough

I am not so sure about this. 30# is a good number, it is what I use too. But I have just dive with a buddy this weekend, where 30# may not be good enough. The issue is he has 28# intergrated into his BC. So it really depends your config. With all weight integrated, you may need more lift on your BC just to flow the rig itself.

How much lift do I need in a BC?

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