View Full Version : tank bouyancy

02-28-2011, 03:27 PM
This might be dumb but ... I've heard that steel tanks are preferred because they stay negatively bouyant from full to empty and aluminum changes from negative to positive. A Catilina 80 CF aluminum goes from -1.8 to +4 while a Worthington 80 CF steel goes from -9 to -3. In each case the difference is (about) 6 pounds more bouyant when empty. What is the difference? Physics & common sense tell me that 6 pounds is 6 pounds. What am I missing?

03-16-2011, 10:17 AM
In my experience, I liked using steel tanks for those reasons, and others, too.

If I was making a beach dive in So. Cal, I would start out shallow and by staying near the bottom, gradually be swimming deeper. So the extra bouyancy of an aluminum tank could play hell with buoyancy towards the end of the dive while swimming into shallower water. (Don't think for one minute that I should just add extra weight, and put air into my BC; That is for rookies!)

I also could get an hour of bottom time or so off a steel 72. It's smaller, and more streamlined shape worked better for me. It didn't make sense in those circumstances to have a larger, bulkier, and inconsistantly weighted tank by using an aluminum 80 (or larger) tank.

Back in the old days, it was easier to fill the "72's" as well.

03-16-2011, 08:08 PM
What am I missing?
Less weight on you belt, I use 300B (4500 psi) tanks which reduce the weigt on your belt even more.