Steel versus Aluminum... is steel better?

[TSandM]

The Al80 in cold water is a pernicious tank. If you compare it with steel tanks with equal empty gross weight, the Al80 is about 5 lbs more positive, meaning that you have to carry five pounds more ballast to dive the Al80. And other tanks, with equal weight and better buoyancy, have more gas. Al80's are plentiful and cheap, but that's about all that you can say about them, and they are not good cold water tanks. On the other hand, technical divers use them as stages, so you CAN resell them. A steel tank will give you more gas, less ballast, and the same or slightly more total weight.

 

[under water]

AL tanks are buoyant when empty, steels don't have that much difference from full to empty.

Dave

Quaack .. this is really wrong. 80 CF of Air will weigh the same whether it is in a steel tank or an aluminum tank. And the swing from a full tank to an empty tank is about 5 to 6 pounds. Steel tanks go from more negative to less negative but should have the about the same swing for the same amount of gas used.

orch1ds .. Yep .. you got it.. More weight for now until you improve buoyancy.

 

[nereas]

So I'm having a hard time keeping my safety stops when my AL 80 tank is about 800 PSI and less. I'm literally inverted kicking with all my might just to not pop to the surface. This is getting to be way too much and I'm scared every time I go deep now because I"m afraid if I get too tired I will just shoot to the top.

When I first bought my gear I didn't know anything about tanks and just bought the one recommended by the dive shop which is my AL80.

I've had no problem with the safety stops when I had about 1500 psi or more. So does this mean I should get a steel tank? Or am I just still too weak in my skills? Probably both?

I have 15 dives now. So clearly I'm still fine tuning... but another instructor I spoke to suggested I switch over to steel tanks.

Can I overcome this or do I really need to now invest in a steel tank and sell my brand new al 80?

Thanks!

Analysis: If you are too light at your safety stop, then you need to add weight.

Choices: To add weight, you may either add weight to your belt, or replace your aluminum tank with steel.

Considerations: If you are diving with a thick wetsuit, then you should not be diving with a steel tank.

Conclusion: You decide!

 

[nereas]

Thanks for the replies everyone. I just had a DUH moment. Weights!

Exactly!

 

[nereas]

The Al80 in cold water is a pernicious tank. If you compare it with steel tanks with equal empty gross weight, the Al80 is about 5 lbs more positive, meaning that you have to carry five pounds more ballast to dive the Al80. And other tanks, with equal weight and better buoyancy, have more gas. Al80's are plentiful and cheap, but that's about all that you can say about them, and they are not good cold water tanks. On the other hand, technical divers use them as stages, so you CAN resell them. A steel tank will give you more gas, less ballast, and the same or slightly more total weight.

A steel tank with a perniciously thick wetsuit is also pernicious, however.

Aluminum tanks are made to go with wetsuits.

Steel tanks are made to go with drysuits.

It works better that way.

And as East is East, and West is West, n'ary the twain should meet.

So you always need to ask the "student" whether they use a wetsuit or drysuit.

 

[MauiScubaSteve]

Frank beat me too it

steels don't have that much differance from full to empty.

Just a little physics here; the swing from full of AIR to 500 psi of AIR is the same amount of weight (AIR) for a same size tank, no matter steel or AL.

 

[nereas]

Frank beat me too it

Just a little physics here; the swing from full of AIR to 500 psi of AIR is the same amount of weight (AIR) for a same size tank, no matter steel or AL.

What do you use in Hawai'i? 3mm wetsuit or 5mm wetsuit?

 

[texdiveguy]

I like both Alm. and St. cylinders.....I have doubles and singles in both materials and dive with both in wet and dry suits.....I have Alm. and St. deco bottles and combine with in dives with both wet and dry suits,,,it all boils down to what you need for a particular dive .

 

[hudson]

Steel tanks are perfectly fine in cold water even with thick wetsuits. There is absolutely no benefit to using an AL tank in cold water instead of a steel: any weight saved on the AL goes right back to your weight belt. There is absolutely no difference in your total weight between the two.

If you can't swim a steel tank up from depth with an empty wing (personally I can, with ease, and I'm by no means in perfect shape) then all you need to do to protect against the unlikely catastrophic BC failure is to carry a few lbs of ditchable weight separate from your main weight belt/harness/pockets, so that once that is ditched you can swim the rig up again (and not rocket to the surface). This is the concept of the balanced rig.

The "disaster" scenario alluded to above can only happen when one is wearing doubles that are heavy enough that the diver carries no additional weight. If you are wearing doubles, one would hope you are aware of how to manage your weight, so it doesn't really apply here.

(yeah, yeah, I know I'm feeding the troll here)

 

[rx7diver]

I agree with several of the others: You should do a proper weight check. Stay shallow when you're doing it (in order to minimize wetsuit compression), say, on the floor at a depth of about 5-10 feet. And do it with a near-empty tank, say, about 300 psig, which, with an Al 80 should be more than enough gas for you to spend a few moments doing your weight check—it doesn't take long—while still leaving enough pressure that water will not enter your tank.

As an aside, I know many divers switch to a steel tank in order to remove weight from their weight belt. In fact, when I first started using steel tanks, this was a major motivating factor for me, too. But, when I began diving solo almost exclusively a few years ago, I convinced myself that a self-reliant diver shouldn't remove too much weight from his weight belt even if he could. After all, he might need to remove his tank and BC at depth (i.e., ditch his gear), maybe to free himself from some entanglement, in which case he should be able to remain approximately neutrally buoyant at depth relatively effortlessly even without his tank and BC. (This also has implications for how thick a wetsuit a self-reliant diver should wear, if he's diving wet, and even the type of neoprene that wetsuit should be made of!) Thoughts anyone?