Buoyancy change with AL vs Steel Tank

[CalgaryDF]

Why is it only normal to add weight to compensate for the air being breathed when using aluminum tanks. Assuming similar volumes of air in an aluminum and steel tank, won't they both undergo the same change in mass due to the air exhaled, therefore leading to the same buoyancy change.

Have I misunderstood the recommendation and you are supposed to add weight to compensate for the air breathed with both tanks.

 

[NorthWoodsDiver]

Take a look at this for some real numbers:

Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400

 

[LeadTurn_SD]

Why is it only normal to add weight to compensate for the air being breathed when using aluminum tanks. Assuming similar volumes of air in an aluminum and steel tank, won't they both undergo the same change in mass due to the air exhaled, therefore leading to the same buoyancy change.

Have I misunderstood the recommendation and you are supposed to add weight to compensate for the air breathed with both tanks.

You've misunderstood. How much weight you need to add is a function of the bouyancy of your exposure suit (and body) versus how negative the tank is (and your other gear). You still need to compensate for the gas consumed during the dive, for either an aluminum or steel tank.

I think what you may have been thinking of is that a steel tank requires you to carry less overall weight when compared to an aluminum tank, but both tank materials require that you account for the "weight shift" that occurs as you consume your gas supply, because the gas itself has weight.

Best wishes.

 

[CalgaryDF]

You've misunderstood. How much weight you need to add is a function of the bouyancy of your exposure suit (and body) versus how negative the tank is (and your other gear). You still need to compensate for the gas consumed during the dive, for either an aluminum or steel tank.

I think what you may have been thinking of is that a steel tank requires you to carry less overall weight when compared to an aluminum tank, but both tank materials require that you account for the "weight shift" that occurs as you consume your gas supply, because the gas itself has weight.

Best wishes.

Ok,
Thats what I thought and what made sense to me. I guess I have remembered/ heard the wrong thing.