Steel tank or Alum?

[alpenadiver]

Because of the cost of steel tanks, I chose a neutrally buoyant aluminium, I dive with both types of AL tanks, and notice quite a difference when they get near empty.

Mike

 

[geraldp]

Because of the cost of steel tanks, I chose a neutrally buoyant aluminium, I dive with both types of AL tanks, and notice quite a difference when they get near empty.
Mike

That's not exactly right... aluminum tanks are not (consistantly) neutrally bouyant. They're negatively bouyant at the start of the dive and positively bouyant at the end of the dive - by as much as 6 pounds depending on the size of your tank.

There's nothing inheritantly wrong with that, but it does mean you have to be careful on your weighting or you could end up shooting through your safety stop in an unsafe ascent (personal experience, I'm embarassed to admit).

There's a chart somewhere on the board (maybe somebody who is more board-literate can post it here for us) that shows the beginning of dive/end of dive bouyancy tables for different tank material/sizes.

All that being said, I agree with the other posters that tanks should be purchased after you get all your personal gear (regs, BC, computer, suit, gloves, hood, etc). Tanks and weights are pretty cheap to rent. In fact in places like Cozumel the tanks and weights are included in the price of a 2-tank dive.

No - the spending on this hobby never stops (especially if you like to buy gadgets but it does slow down. I finally bought a pair of PST E7-100's a couple of months ago. With Nitrox cleaning they were closer to $330 apiece at my LDS. Finally after 18 months of diving I now have all the gear I need to go diving without renting anything.

Jerry

 

[yknot]

That's not exactly right... aluminum tanks are not (consistantly) neutrally bouyant. They're negatively bouyant at the start of the dive and positively bouyant at the end of the dive - by as much as 6 pounds depending on the size of your tank.

There's nothing inheritantly wrong with that, but it does mean you have to be careful on your weighting or you could end up shooting through your safety stop in an unsafe ascent (personal experience, I'm embarassed to admit).

Jerry

Stop and think about the physics behind this argument. The only difference between a "full" tank and one at 500 PSI is the weight of the air. If your alum tank was, say, 2 lbs pos at the end of the dive and held 8 lbs of air, we could deduce that it was 6 lbs neg at the start. Applying this same argument to a steel tank, lets say it ends up (at 500 PSI) at 2 lbs neg. Along with the same 8 lbs of air, it will start out 10 lbs negative. Proper weighting plans for the end of the dive (that 500 psi or less event) so that a diver can be neutral or negative during a safety stop, but definately not positive. With the two examples above, the real difference would be that diving the steel tanks, a diver has 4 lbs less on their belt/in BC pockets and instead has the weight on their back. Lastly, some people don't like the characteristics of bouyant alum. tanks at the end of a dive but this is also partly due to how your weight is distributed.

 

[alpenadiver]

According to Luxfer a empty standard AL-80 has a salt water buoyancy of +4.40 lbs.

While a empty Neutrally buoyant AL-80 has a salt water buoyancy of +0.05 lbs

although this might not mean alot if you dive with steel, anything that means less lead on my body equals