Help with wing lift calculation
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runsongas
Contributor
3 percent of total displacement, that also includes the weight and volume of the diver
For those who (unlike @49north) did not manually measure the buoyancy of their exposure suit, I have edited the Lift Calculator spreadsheet to add a page to estimate buoyancies of a variety of exposure suits. Enter your height, weight and wetsuit thickness, and the spreadsheet will give you an estimated buoyancy based primarily upon body surface area. Enter the type of drysuit liner, and you will have an estimated drysuit buoyancy. Just plug this number into the Lift Calculator to see what the adequacy of your wing is at depth or on the surface, and what redundant lift you might need with a torn wing.
Cheers!
Cheers!
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Well, since we're nitpicking, not quite...
You did your neutral buoyancy at eye level, so drop that 8-10# of cranial weight to 4-6#.
You did your neutral buoyancy at mid-lung volume, so inhale and you'll be fine.
Or roll onto your back.
@KWS makes a good point - don't cut things too fine. But if you need 16.5# of lift and you buy 23#, you're just fine. You only needed that 16.5# at depth with suit compression. With a fully expanded wetsuit on the surface, you have plenty of extra lift. Check the spreadsheet.
Flooded drysuit - different story. But that wasn't the question here.
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If you are weighted to be neutral at 20 feet with 500 psi, then you will be just the slightest bit positive at the surface with 500 psi with a wetsuit or neutral with no compressible buoyancy. In that case, you only need a 12 lb wing: 6 to float your full tank, 5 for your plate, and 1 for good measure. Add a little more lift for things like lights and heavy cameras.
If all of your weight is on your rig, you'll need enough lift to counter that. If all your weight is on your belt, your exposure suit will counter that at the surface, especially if you are balanced by a negative rig when the wing is empty.
At depth, with compression of your suit, you'd need to be pretty deep in a pretty big suit to really need 23lb of lift. And if you have a failure immediately, with a full tank, a reasonably good swimmer, as any diver should be, can drop a ten pound belt and swim up the rest. As a 12 year old boy scout and then again as a lifeguard in college we had to retrieve a 10-12 pound weight off the bottom of the pool and hold it above our heads at the surface. You'll have the buoyancy of the suit at the surface.
In salt water, everything buoyant will be more buoyant, but really, only the change in the suit's buoyancy needs to be compensated for at depth because your body doesn't compress.
I deliberated long and hard and talked with Bryan about it. My 23# wing ships tomorrow.
Jay
Need to dive more!
These are good points and how about if your buddy's BCD tears, you're both at depth and don't wish to ditch any weights* or fluff around with a DSMB.
I only dive topical in a 3/2 (input as 2.5), AL80, 12# and the modified spreadsheet tells me I might need 12# (with no weight drops), and if my buddy's rig is similar and her BCD fails then isn't 23# 'marginal'? (for me)
(*reasons, so you don't compound/cascade problems with a possible uncontrolled ascent, who ditches, how much, what if buddy isn't thinking straight ... etc)
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