Steel or Ali?

[tankboygreg]

Steel

As the original poster notes Aluminum has some niche applications where it has an advantage. My whole rant is here: http://home.gwi.net/~spectrum/scuba_al80.html

Pete

Per your website:

"As mentioned, an AL-80 has 4.4 pounds of positive buoyancy when empty. Meanwhile a PST E7-80 will be 2.5 pounds negative when empty. 4.4+2.5 = 6.9, call it 7 pounds of difference in buoyancy. The aluminum tank is a liability since you need to add weight to hold it down at the end of the dive. The steel tank contributes to keeping you and your exposure suit down. The 7 pounds represents 7 pounds of weight you do not need to wear when diving a PST E7-80. This comes right off your belt. "

You still have to contend with the 7 pounds of difference in bouyancy at the the end of the dive. Whether you have an aluminum tank or steel tank air weighs the same and you are going to get 7 pounds lighter over the course of the dive. Either way you have to compensate for this.

 

[Buoyant1]

My instructor turned me on to steel since I started diving in the 7mm with hood, gloves, etc. Takes 10 lbs out of the BC! (plus since they are 120's they have a whole lotta Nitrox to breath!)

I plan on purchasing either a steel 119 or 130!

 

[echo5506]

Steel absolutely. Less weight to carry and longer dive times.

 

[Packhorse]

I dive with aluminium tanks less weight

Really? What size and weight tanks do you use?

 

[fdog]

<snip>
You still have to contend with the 7 pounds of difference in bouyancy at the the end of the dive. Whether you have an aluminum tank or steel tank air weighs the same and you are going to get 7 pounds lighter over the course of the dive. Either way you have to compensate for this.

Aluminum cylinders are +4.4 lbs bouyant when empty. You have to add this lead to your belt.

Steel cylinders are -2.5 lbs bouyant when empty (they sink). This is lead you can remove from your belt.

Spectrums' comparison refers to the bouyancy of empty cylinders, and indicates the amount of lead you can remove from your belt by switching from aluminum to steel.

Gas does have weight, however it is equal in this comparison (at roughly 5 lbs). Anyway, since the starting figures are for empty bouyancy, the gas weight is irrelevant. Correct weighting assumes empty cylinders at the surface.

All the best, James

 

[spectrum]

Per your website:
You still have to contend with the 7 pounds of difference in bouyancy at the the end of the dive. Whether you have an aluminum tank or steel tank air weighs the same and you are going to get 7 pounds lighter over the course of the dive. Either way you have to compensate for this.

Nowhere in my discussion do I deal with the effiect of breathing the tank down since that is the same of any cylinder of same volume. Aiir depeletion along with the varriations in neoprene buoyancy are why we wear a buoyancy compensator. It will begin the dive supporting the mass of your air supply and will be relieved of this load as you consume your air.

BTW at .08LB/CF the entire air mass of an 80 CF fill is 6.4 pounds. Most divers will see a 5-6 pound shift over the dive, not 7.

Pete

 

[Jason Ooi]

11 lt ali tanks for back and ali for deco and stage 7 lt tanks

Really? What size and weight tanks do you use?

 

[DivingCRNA]

I'm a new diver, only 19 logged at this point. About 1/2 are cold water ocean dives and I find I prefer the steel tanks. I think the biggest reason is the -bouyancy during my safety stops. Plus less weight I need, although still working on my trim alot. I also have been diving with my 19cf pony almost every dive too. Things might change as I become more experienced though.

Here is the thing that still puzzles me about this arguement:

All tanks weight less empty than full. You lose the weight of the air in the tank when the tank empties during a dive.

So, even if you are diving steel, which is still negatively buoyant when empty, your tank weighs less at the end of the dive. If you are not weighted for an empty tank, and you have an empty tank strapped to your back (along with buoyant exposure protection), you can still be positively buoyant at the end of the dive and struggle during deco/safety stops.

It would seem to me that ensuring correct weighting for the END of the dive would solve this problem in most circumstances.

You can even solve the trim problem by putting weight on the tank straps or your backplate. It shouldn't matter that this weight is non-ditchable because it is as ditchable as the steel tank is.

Or I could just be wrong. Which is definately possible.

I can definately see the volume advantage of steel for long dive plans, though...

 

[DivingCRNA]

Steel absolutely. Less weight to carry and longer dive times.

You still carry the weight, just not on your belt/in your BC. It is on your back.

 

[BHB ScubaTroll]

what do you prefer to dive with? Steel or Ali, most people I meet say steel as their deco is easier than with an empty Ali.

What do you all say about it?

Stupid Poll.
I have 6 AL and 4 steel. It depends on the diving I do.

4 AL are standard air
2 AL are nitrox (selling)
2 Steel 133 (nitrox)
2 Steel 149 (nitrox)

dive what you need