Calculating buoyancy of a BP/W

[twistypencil]

Hi all, I've been reading old threads about buoyancy calculation, and found the spreadsheet that someone made, which is supposed to be easy to use, but I'm positively confused and negatively flummoxed.

How do I find the volume and weight of my BP/W system? I've got a Hog 32lb 360 Bungee Wing, DiveRite stainless steel backplate, your regular old harness+crotch strap, and a couple cambands.

I found a nice android app called "Lead" that is simple to use, you just add all your gear, and it helps you understand... but they don't have any BP/W system on there, nor any flippers, gloves or boots, or computer. I can add them, but I need to know what their "volume" and weight are to add them.

 

[tbone1004]

buy a cheap luggage scale, put it in the pool and weigh it.

alternatively it's about 6lbs negative and that's certainly close enough

 

[twistypencil]

32lb stainless steel BP/W: -6lbs ?
7mm wet: 10% body weight (175-180) + 6lbs: +24lb
7mm step in hooded vest: +11lbs?
7mm boots: ?
7mm gloves: ?
Full set of regulators (1st, 2x, octo and gauge): 4lbs (negative, or positive?)
Computer: ?
Alu80 tank with 3000 PSI (salt): -1.5lbs
Alu80 tank with 750 PSI (salt): +3lbs
Steel80 tank with 3000 PSI (salt): -13lbs
Steel80 tank with 500 PSI (salt): -8.5 pounds
Fresh water: ?

 

[broncobowsher]

Weigh it empty. Fill the wing with water, weigh it again. That is the weight of water that can be displaced with air when in water, hence lift. You are just figuring it the other way around (water in air instead of air in water).

 

[tbone1004]

you are only going to get accurate numbers by weighing everything and doing a proper weight check unfortunately. no way to do theoretical calculations

 

[twistypencil]

Weigh it empty. Fill the wing with water, weigh it again. That is the weight of water that can be displaced with air when in water, hence lift. You are just figuring it the other way around (water in air instead of air in water).

Isn't a 32lb wing going to just provide 32lbs of lift (ie. +32lbs buoyancy?)

 

[SJT1961]

@TBone: would it be better to weigh in pool or saltwater?

 

[Bowers]

weigh it in what you will be diving in

 

[broncobowsher]

Isn't a 32lb wing going to just provide 32lbs of lift (ie. +32lbs buoyancy?)

My understanding it that it is strictly a displacement calculation. No telling what the wing will be attached to for a backplate or harness. A lightweight carbon fiber backplate, or a super thick stainless one? That will change the lift of the package. If you take a wing, all by itself, completely deflated, it will be close enough to neutral in water to be meaningless.

 

[twistypencil]

My understanding it that it is strictly a displacement calculation. No telling what the wing will be attached to for a backplate or harness. A lightweight carbon fiber backplate, or a super thick stainless one? That will change the lift of the package. If you take a wing, all by itself, completely deflated, it will be close enough to neutral in water to be meaningless.

As I mentioned in the initial post, i've got a 32lb stainless steel backplate.