Quiz - Physics - Minimum Amount of Water That Must Be Displaced

[EFX]

Typical Al80s hold 77-78 cu.ft. of air at rated pressure. Unless you are cave-filling your Al80s (not recommended), the maximum buoyancy swing you will see is a little over 6lbs (6.2) if you are sucking them dry. Al80s don't have a 10lb buoyaSteel ncy delta.

You are right. I should have checked the numbers first. Instead I went by (bad) memory. I found a Luxfer AL80 tank buoyancy swing at -1.4 to +4.4 lbs.

 

[-JD-]

You are right. I should have checked the numbers first. Instead I went by (bad) memory. I found a Luxfer AL80 tank buoyancy swing at -1.4 to +4.4 lbs.

No worries. I see the same figures. And sometimes I just don't .... What was I saying?

 

[Storker]

Only on SB can a simple theoretical buoyancy problem spawn 3 pages of discussion after the answer has been provided.

 

[tursiops]

.

 

[Frackingawesome]

It does not matter cause i aint no pussy and would just swim that **** up to the surface!

 

[Frackingawesome]

You give it a little tug, and up it goes

Also that is what she said...

 

[Rickk]

I should have added this question to the list, since something like it appears regularly on ScubaBoard.

• At the beginning of a dive Diver A and Diver B are both 9 pounds negatively buoyant. Diver A's steel cylinder weighs 5 pounds more than Diver B's aluminum cylinder. During the dive, both divers consume 5 pounds of air. What are their buoyancies at the end of the dive?

It would be interesting to see the answers for this question.

They are both 4 lbs negative assuming no difference in the air in their BC from start to end of dive. The weight of the tank does not matter, how much lead they have and how buoyant their bodies are does not matter. AAll that matters is the change in weight during the dive and in both cases it is 5 lbs less air.

 

[Rickk]

Although that may happen, it is not because of buoyancy if the tank. I found that the old stab jackets and to a lesser degree the newer poodle jackets, the tank being lighter at the base as it loses air, will pull up the back of the jacket making the air bubble shift back and up, which will have the gas expand and possibly drag you up if you didn't correct early. ....

I am sorry but the position of the gas in the BC does not impact buoyancy that much. Perhaps if the shifting caused a slight increase in the height of the gas bubble it would expand but at any depth beyond a couple m the amount of expansion due to a diver rotating from horizontal to vertical will be minimal.

The shifting gas in the BC or in a dry suit will impact trim but unless accompanied by a change in depth will not impact buoyancy.

 

[SimonMirr]

b. 60L (to be neutral):

175 - 115*1.03 = 60

Got that formula from the RAID training manual which I believe is very similar to PADI (manual wise).