@Remy B.
What
@Patoux01 said is correct as well. If you are diving in a drysuit, the gas in the wing should only be the gas content of bottles. It's going to be big regardless of if you have 6x al80's, or 2x19l/lp121's and 2x 80's. If you are weighted properly, it is the same amount of gas.
How to calculate buoyancy of a scuba cylinder (metric)
Material:
Steel
Capacity: 11 litres
Working pressure: 200bar
Weight: 15 kg
Diving in: Fresh Water
Using Archimedes principle, buoyancy is equal to the weight of the displaced water minus the weight of the cylinder.
The cylinder is made of
15 kg of steel, (which has a density of 7.8 kg/litre).
The steel therefore has a volume of 15 / 7.8 = 1.92 litres, so the total volume is 11 + 1.92 = 12.92 litres.
The density of fresh water is 1 kg/litre, giving 12.92 x 1 =
12.92 kg
Air has a density of 0.0012 kg/litre.
The air in a full cylinder weighs 0.0012 x 200 bar x 11 litres =
2.64 kg.
The cylinder when empty has a buoyancy of 12.92 kg - 15 kg =
-2.07 kg
The cylinder when full has a buoyancy of 12.92 kg - 15 kg - 2.64 kg =
-4.71 kg
NB - these figures exclude valves, manifolds, regulators, etc..
Material:
Aluminium
Capacity: 11 litres
Working pressure: 200bar
Weight: 13 kg
Diving in: Fresh Water
Using Archimedes principle, buoyancy is equal to the weight of the displaced water minus the weight of the cylinder.
The cylinder is made of
13 kg of aluminium, (which has a density of 2.7 kg/litre).
The aluminium therefore has a volume of 13 / 2.7 = 4.81 litres, so the total volume is 11 + 4.81 = 15.81 litres.
The density of fresh water is 1 kg/litre, giving 15.81 x 1 =
15.81 kg
Air has a density of 0.0012 kg/litre.
The air in a full cylinder weighs 0.0012 x 200 bar x 11 litres =
2.64 kg.
The cylinder when empty has a buoyancy of 15.81 kg - 13 kg =
2.81 kg
The cylinder when full has a buoyancy of 15.81 kg - 13 kg - 2.64 kg =
0.17 kg
NB - these figures exclude valves, manifolds, regulators, etc..
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Lets take a example of 4 AL-11L vs 4 Steel 11L both at 200bar, assuming you need 8kg to be neutral yourself with your dry-suit and thermal protection
4 AL, assuming worse scenario of emptying completely = 4 x +2.81 requires 11.3kg to be neutral
4 Steel. assuming the same scenario, = 4 x - 2.07 requires only "cero" kilos but still will be 0.28kg negative
but at the beginning of the dive with tanks full
4 AL will = 4 x +0.17kg = +0.68kg -11.3 = -10,6 Kg
4 Steel will = 4 x -4.7kg = -18.8kg + -0.28 = -19.08Kg
I took the weight from AL and Steel manufactures.
I don't buy this reasoning from both of you, your wing or dry-suit will look like a balloon at the beginning of the dive if using steel tanks, because you have to compensate for that extra weight of the tank material as well not only the gas content.
You are new to proper weighting and what it involves, right? The amount of air in a wing is not a matter of what the tanks are made of. It's a matter of their content.
What Patoux01 said is correct as well. If you are diving in a drysuit, the gas in the wing should only be the gas content of bottles. It's going to be big regardless of if you have 6x al80's, or 2x19l/lp121's and 2x 80's. If you are weighted properly, it is the same amount of gas.
If I understand incorrectly, please correct me.
Source
https://www.subaqua.co.uk/cylinder-...l=steel&volume=&pressure=&weight=&water=fresh