Why Steel tanks are preferred for doubles?

[ScubaG]

I think the most common reason for using steel cylinders for doubles is their favorable buoyancy characteristics. i.e. negative or neutrally buoyant when nearly empty.

So with this reasoning, one could setup for eg. AL 80s as doubles too and for their positive buoyancy characteristics, could use tank weight pockets mounted on the tanks to counter to their positive buoyancy.

The main advantage I see of this is mainly the COST of Aluminum over the pricy steel cylinders. So what are other pros & cons of using AL for setting up doubles?

G.

Aluminum 80s are too small. At 3000psi you only get 154 cubic feet of gas (77 each). Steel 95s are usually pumped to 3600psi, and you get 260 cubic feet (130 each). Steel 104s are probably the most common cave doubles, and they carry 280 cubic feet. Even low pressure 80s carry 218 cubic feet, and are smaller than aluminum 80s.

Aluminum cylinders have one, and only one, advantage: price. But when you consider cave divers probably average $5,000 worth of gear on their person when they dive, why use an inferior set of doubles to save a couple hundred dollars?

About the only time you'll see aluminum cylinders in caves is for stage bottles, where the relatively neutral buoyancy is preferable.

Russell

[ScubaG]

Aluminum 80s are too small. At 3000psi you only get 154 cubic feet of gas (77 each). Steel 95s are usually pumped to 3600psi, and you get 260 cubic feet (130 each). Steel 104s are probably the most common cave doubles, and they carry 280 cubic feet. Even low pressure 80s carry 218 cubic feet, and are smaller than aluminum 80s.

Good Point..I did not think about that aspect.

[DeWayne]

With my 85's pumped up I enter the water with about 240cft of air, at basically the same or less weight that AL 80's would be at. While AL is much cheaper, the steels will far outlast them.

[D1V3R]

yeah, I really don't like using aluminum cylinders; if I only need 80 cu. ft. I use a high pres. steel tank, and it's like 2/3 the size of an aluminum 80.

[normblitch]

With my 85's pumped up I enter the water with about 240cft of air, at basically the same or less weight that AL 80's would be at. While AL is much cheaper, the steels will far outlast them.

While I'm not as adventuresome as Doc Dee (I only pump my 95 single to 120 cubic :roll: ), I am SO happy to be done with AL80's for overhead. I wanted a tank that would give me TWO fulfilling cavern/Basic dives on one fill, and I sure got it in my steelie!

In General Aviation, the three MOST useless things are 1) runway BEHIND you, 2) altitude ABOVE you, & 3) air IN your fuel tank...for DIVING add LEAD of any kind attached to you. Can't breath it, can't take pictures with it...

In my now & again interest in SM, I occasionally think of using my two AL80's to get aquainted with the idea & rigging. Doing the math as above, with the exception of redundancy, all it would gain me (2 x AL80 vs. single 95) is ONE THIRD of 40 cubic feet. IMHO, probably not worth it...

Norm
world's oldest living Cavern Diver

In General Aviation, the three MOST useless things are 1) runway BEHIND you, 2) altitude ABOVE you, & 3) air IN your fuel tank

I thought the most useless thing in aviation was five seconds ago.

Russell

[normblitch]

In General Aviation, the three MOST useless things are 1) runway BEHIND you, 2) altitude ABOVE you, & 3) air IN your fuel tank

I thought the most useless thing in aviation was five seconds ago.

Russell

DUTIFULLY ADDED...

( I LIKE that one!)

nhb