Posted by Chirs on June 30, 2003 at 00:18:00:
In Reply to: Re: Diving Refugio Beach/Steel 95/100 v. Al 80 posted by Randy on June 29, 2003 at 23:08:25:
Actually the change in buoyancy is the same for all tanks of equal capacity. 80 cu.ft. of air weighs the same no matter what size or material of tank you put it in.
That being said, the buoyancy characteristic of tanks is different. Al80s can be up to 5 pounds buoyant at the end of a dive, this means you need to compensate for them by adding weight to your belt. Most (but not all) steel tanks tend to be neutral or negative at the end of a dive. This means you will need less weight on your belt with the steel tank.
To determine how to change your weighting with different tanks get a trashcan and fill it with water. Then empty your tanks until they each have about 500 psi in them. Then put them in the water and weigh them with a scale. For the Al tank you will probably need to add some weight. This weight difference at 500 psi is the amount you adjust your weighting up or down with the new tank.
For beach dives my favorite tank to use used to be a steel 72. However I now use HP80’s these tanks are about 1½ negative at the end of the dive, but are much nicer to use. They are a bit lighter, they are smaller, and just nice beach dive tanks.