Nice and simple question about wings

[Far_X]

If a wing has a 45lb lift - what does the 45lb actually measure? Is it the weights + negative buoyancy of tanks + equipment? "The Fundamentals" states that a single tank should not be more than a 30lb lift and a double tank set up should not be more than a 60lb lift. But a heavier diver requires more weight to offset his/her more positively buoyant body and more weights are required when wearing a dry suit so are they taken into consideration for a formula? Thanks for your answers.

 

[The Kraken]

Hope some others jump in here, but I would surmise that a bladder, when inflated to it's maximum inflation capacity, ie 30#, would support 30# of dead weight at the surface.

 

[Far_X]

and "dead weight" is the result of the positively buoyant items subtracted from the negatively buoyant items?

 

[The Kraken]

Well, the way if figure it, if you had a BC of 30# lift and you inflated it completely, hung a 35# weight on it and put it in the water, it'd sink. Or if you put a 30# weight on it, it would be neutrally buoyant at the surface.

 

[Spectre]

your wing offsets two things... the weight of the gas in your tanks and the weight you needed on the surface to offset the bouyancy of your exposure protection that is lost at depth by the compression of the suit.

Everything else should be balanced to neutral.

The weight of the gas is weight that won't necessarily be there at the end of the dive; so at the beginning of the dive you are overweight by the weight of that gas. That you need to be able to compensate against with your wing.

Likewise you need weight to compensate for the positive buoyancy of your exposure protection. If that exposure protection compresses at depth, then you end up being overweighted by the amount of weight used to compensate for the compression of the suit.

 

[utnapistim]

hi

those 45lb lift mean that once you're neutrally buouant, you could hang 45lb of lead on you, inflate your bc and still be neutrally buoyant. ( I guess )

 

[detroit diver]

Someone did a test a while back on the actual lift of various wings. If I remember correctly, none of them actually supported their rated weight when tested. I'll try to find the info on a search, but it was a long time ago.

 

[FreeFloat]

Interesting, considering my Halcyon snigle-tank wing is 'rated' at "36" pounds......... I'd be interedted to see what its 'actual' lift is.

I had sort of been wondering the same, myself..... as in "what exactly is the 36 pounds it's supposed to lift?"

 

[cool_hardware52]

Wing lift, how to measure and what does it actually mean.

If I secured a spring scale (fish weighing scale) to the bottom of the pool / ocean / lake etc. and attached a BC of X lbs lift to it and inflated it fully, the reading on the scale would be the max lift that wing could generate.

(Some may weigh in here and point out at greater depths the density of the air in the BC is higher and this reduces the lift, true, but by trivial amounts.)

To say a 40lb wing will neutral if you attach 40lbs of lead is not true. Lead weighs 708 lbs per cu ft and water is ~63 lbs cuft., so lead submerged in water is 708-63 = 645 lbs / cuft. Your 40lbs of lead, submerged in water is about 36 lbs negative because it displaces .056 cuft of water.

How do manufacturers determine lift? Do they use a fish scale and a pool? In a word no.

To determine the lift of given bc, blow it up fully and weigh it, then fill it with water and weigh it again. Subtract the two values and bingo........you got the lift for that wing.

A couple more points.

Very small variations in stitch path can cause significant variations in the effective size of a wing. Quite common to find BC's that are + - 20% of their rated lift, due to manufacturing induced variations.

If accurate lift values are vital. i.e. you might be close to exceeding the avaiable lift, a further test is necessary, especially for wings.

Wings can be constrained by both the tank and the backplate. Different tanks or set of tanks can constrain the wing differently. Imagine a short 63 snuggled into the center of a "donut wing" vs a longer tank. The wing can be constrained by the longer tank. This is more profound if one considers using a wing for both single tanks and doubles. A wide set of doubles can trap a big chunk of bladder between the plate and the tank, bad news because doubles generally dictate more, not less lift.

How do you test for this? Simple just build up your rig as you would dive it and rerun the test described above. You may be surprised...


Regards,




Tobin

 

[MXGratefulDiver]

"The Fundamentals" states that a single tank should not be more than a 30lb lift and a double tank set up should not be more than a 60lb lift.

Based on my personal experience, I would have to say this statement is not applicable in all situations. No way can I dive my singles rig with just a 30-lb wing ... I've tried it and it simply isn't enough to support me and my rig at the surface (required constant kicking to stay on the surface). I now own a pair of 45-lb wings for my singles rigs, and they're just right.

Now ... if I were diving in warm water, with a 3-mil wetsuit and AL80 cylinders, a 30-lb wing would probably suit me just fine. For cold water diving and a larger cylinder, it just won't cut it ... especially in conditions that require frequent, long surface swims.

... Bob (Grateful Diver)