Cylinder type and proper weighting (SPLIT FROM 'Pull Dumps - Lose them')

[boulderjohn]

density is what affects bouyancy, aluminium has a density of 2560 lb/ft3 steel is 7850 lb/ft3

I see. Archimedes Principle is not involved after all. Weight and volume are not part of the equation.

So are you saying a steel-hulled ship will sink while a block of solid aluminum will float?

 

[gcarter]

Y

you need to look at the chart you posted every single one of the steel tanks have a negative bouyancy Empty. density is what affects bouyancy, aluminium has a density of 2560 lb/ft3 steel is 7850 lb/ft3

What do you think density is if not the relationship between weight and volume?

 

[Celt]

I think this is a waste of time but OK, once more. A rock has buoyancy. Try diving with 10 lb of rock for weight when you need 10 lb of lead. It won't work because even though rock sinks it has more buoyancy than lead. A steel 100 weighs about 8 lb less when empty than when full. It displaces the same amount of water when empty or full so it has less buoyancy when full, even if it sinks when empty. For you to be neutral in the water, neither sinking or floating up you will have to change your weighting 8 lb between a full tank and an empty one. You do that by carrying enough lead to hold you down with an empty tank, OK, split hairs, an almost empty tank and you offset that extra weight by putting air in your BCD when the tank is full. I understand that you can also keep more air in your lungs instead of air in the BCD, or you can swim up slightly when the tank is full, or you can breath at the bottom of your lungs when the tank is nearly empty, or swim down when the tank is nearly empty. Something has to offset the weight of the air that you breath during the dive. As you get bigger and bigger tanks I.E. 130 cubic foot tanks (10+lb of air) this difference becomes very apparent and hard to offset by breath control or swimming slightly up or down.

steel tanks have negative bouyancy empty or full. you do not need any lead to sink a steel tank. aluminium tanks at best are neutral and worse very buoyant,you have to carry more lead, the weight of twin 7ltr or twin 10ltr change very little over the course of the dive.and the extra weight can be used to offset the bouyancy of your suit or jacket.

 

[Steelyeyes]

I'm keeping my pull dump.

 

[Celt]

I see. Archimedes Principle is not involved after all. Weight and volume are not part of the equation.

So are you saying a steel-hulled ship will sink while a block of solid aluminum will float?

where did i say that,

 

[Celt]

What do you think density is if not the relationship between weight and volume?

I know exactly what density is do you?

 

[boulderjohn]

you do not need any lead to sink a steel tank. aluminium tanks at best are neutral and worse very buoyant,you have to carry more lead,

I will repeat what I said before.

When I taught classes in a pool with a 3 mm shorty and an aluminum tank, I did not need any lead at all. When I dived in a dry suit with a steel tank, I needed lots of lead.

The need for lead is based on the entire package--the water you are in, your thermal protection, your body composition, your gear, and your tank. The tank is only one part of the equation. It is not the sole determining factor in deciding whether you need lead.

Yes, if you are using an aluminum tank, you are more likely to need more lead than with a steel tank. SO WHAT?

I have said this probably 8 times now, so I will drop out of this scintillating exchange.

 

[Celt]

I think you have the unit of measurement of density mixed up. Those numbers are for kg/L or g/mL, not lb/ft3. You need to multiply them by 62.4 to convert the numbers into lb/ft3. Density of water = 1 kg/L = 62.4 lb/ft3.

And go back & study: Archimedes' principle - Wikipedia

hands up your right, should be kg/m3

 

[Celt]

I will repeat what I said before.

When I taught classes in a pool with a 3 mm shorty and an aluminum tank, I did not need any lead at all. When I dived in a dry suit with a steel tank, I needed lots of lead.

The need for lead is based on the entire package--the water you are in, your thermal protection, your body composition, your gear, and your tank. The tank is only one part of the equation. It is not the sole determining factor in deciding whether you need lead.

Yes, if you are using an aluminum tank, you are more likely to need more lead than with a steel tank. SO WHAT?

I have said this probably 8 times now, so I will drop out of this scintillating exchange.

thanks John i enjoyed the debate.

 

[Dan]

hands up your right, should be kg/m3

Oops. I didn’t have my glasses on. Now I put my glasses on, I didn’t see any decimal point in your numbers. So I’m off by 1000x. My bad. I’m more wrong than you were. LOL.