Posted by Chris on September 27, 2001 at 09:11:26:
In Reply to: tank buoyancy posted by Chuck on September 27, 2001 at 02:41:22:
The tank manufacturer, Pressed Steel, has a chart that is very close to what I have measured myself at http://www.pstscuba.com/aaspo.htm
I have found that most of the published charts are wrong, so I do my own measurements.
I like to adjust my buoyancy so it is the same at 500 psi, thus I can always make my safety stops in the same manner.
To do this, I fill up a trashcan with water, and then weigh the tank with 500 psi in the water, using a fish scale.
Although there is a slight difference in density between fresh and salt water, it is so small you will not be able to measure the difference with a fish scale.
For some tanks, like AL80s you will need to add some weight to make the measurement since they are buoyant.
All my HP tanks are Pressed Steel.
My HP120's are neutral at 500 psi.
A HP100 is about 1 lb. negative at 500 psi.
The answer to your question depends on how much that 1lb buoyancy difference means to you:
Answer #1: add 1 lb. on your weight belt.
Answer #2: don't worry about it, 1 lb. of difference is not a big deal.