Any reason to not go steel?

[xiSkiGuy]

you are not "saving" weight, just moving it from your hips to your back.

That is not entirely true. Don't confuse dry weight with buoyancy.

For instance, a Luxfer AL80 weighs about 31lbs empty. So does a Faber LP-85. If you tossed each of those empty tanks into the water, the AL80 would be 4.4lbs positive and the LP-85 would be neutral. That is 4.4 pounds in extra lead you wouldn't have to carry on your weight belt if you switched to the LP-85.

 

[nereas]

I am a New England diver. I wear a full 7mm wetsuit and accessories. I have been diving with aluminum tanks (got them for free) but want to ditch some of the lead I have to carry because of it. So, I am kinda' commited to buying steel tanks but had a final question before I wrote the check.

Is there ever a time when you want the bouyancy of the aluminum tank? Let's say you were diving in warmer water and using just a 3mm wetsuit (perhaps a shorty) is it possible that you could be overweighted with a steel tank? I mean, isn't it inherently unsafe to not have any lead to dump to create positive bouyancy? Would you then be relying on the BCD to keep you from sinking and prone to problems if the BCD failed?

Maybe I'm over-thinking (my tendancy) but I am just curious about any possible pitfalls.

Thanks in advance!

Steel tanks last forever, if you care for them properly, and make sure no water gets inside of them during the refill process (such as on a boat).

Aluminum tanks are subject to stress fractures at the threaded end.

With a wetsuit, there is a theoretical basis for diving with aluminum tanks, since at depth these tanks tend to become slightly positive as they are depleted of air/nitrox. Since the wetsuit compresses at depth, you need very little weight if any to be neutrally buoyant at depth, maybe only 4 to 6 lbs while wearing a compressed wetsuit at depth.

Your regulator system will comprise about 2 to 3 lbs of negative/weight. (I hate to say "negative buoyancy" because that is a contradiction in terms, technically speaking.)

This leaves you with only about 3 lbs available for nonditchable negative/weight.

Here are your choices for the remaining nonditchable negative/weight:

1) aluminum backplate 2 lbs -or-
2) single steel tank 0 to 2 lbs -or-
3) small cannister light 2 to 3 lbs.

As you can see, it is a very short list. Note that as was pointed out above by xiSkiGuy, an LP-85 would be neutral when empty, however. This would give you a little more leeway, but not much.

If you marry an aluminum tank with a steel backplate, you have virtual neutral buoyancy between the two. This beats the 6 to 8 lbs negative weight of a steel tank and steel backplate. Of course, with a steel LP 85 and an aluminum plate, you are only negative by about 2 lbs plus the weight of the air/nitrox (0.08 lb per cu ft).

If you decide to over-weight yourself, then you should make sure and get a double-bladder wing. The good news is that Oxycheq does indeed manufacture and sell these! www.oxycheq.com

The bad news is that with a double-bladder wing, everyone on the beach or boat will look at you like you are some kind of dinosaur with 2 inflator hoses running down left and right, and some people will not even go diving with you then.:no

Good luck, in your choices.

 

[Colliam7]

I am a New England diver. I wear a full 7mm wetsuit and accessories. I have been diving with aluminum tanks (got them for free) but want to ditch some of the lead I have to carry because of it. ... Is there ever a time when you want the bouyancy of the aluminum tank?

Your post suggests you are not replacing AL tanks with steel, only that you are adding some steels. Diving a single steel, even a 130, with a standard or back-inflate BCD is unlikely to make you so negative that you could not swim the tank up even with a BCD failure. If the majority of your diving is cold water with a 7mm, then a steel seems reasonable. While rust might be an issue, an annual VIP and filling at a reliable station should help manage that (I have had two 120s for over 6 years, that I now VIP myself, and they are clean. There are few disadvantages compared to the advantages accrued with thick neoprene.

 

[Jim Lapenta]

I just got an HP steel 80. I am thinking I can drop about five pounds from my weight pockets. Does this sound like a reasonable amount? I'm a slim female.

It would depend on the type of BC you use, exposure suit, your comfort level, and were you properly weighted to begin with? I was able to drop about 6-8 lbs when going from an al80 to an HP80. When I went to a BPW I was able to use no weight even with a 5 mil in fresh water. Not saying much as I was only using 4 lbs anyway with that suit and a jacket bc. Best thing is get in the pool or some other area if diving saltwater and do a weight check. You need to remember that the 80 will go from 8lbs neg to 1 1/2 lbs neg at 500 psi or so. An Al80 goes from 8 neg to about 4 positive. Much bigger swing.

 

[GreenDiverDown]

You need to remember that the 80 will go from 8lbs neg to 1 1/2 lbs neg at 500 psi or so. An Al80 goes from 8 neg to about 4 positive. Much bigger swing.

Better re-think that one, Jim.

How much air ya got in each cylinder?

 

[Scubakevdm]

I just got an HP steel 80. I am thinking I can drop about five pounds from my weight pockets. Does this sound like a reasonable amount? I'm a slim female.

Maybe six.

 

[Bratface]

JimLap, Scubakevdm, thanks for the info.

 

[GreenDiverDown]

The "swing" of a cylinder has nada to do with the material from which the cylinder is made. It is only a function of the amount of the gas. In this case, the amount of gas in each cylinder is almost the same... a steel HP 80 holds 80 cuft at its rated pressure and an Al80 holds 77.4 cuft.

The weight of dry air at 1 ATM and 20 degrees C is about 0.075 lbs per cuft. So... both cylinders hold about 6 lbs of air. (0.075 x 80) The "swing" is the difference in buoyancy between a cylinder when it is full vs empty and in this case is the same for both cylinders.

The buoyancy of a steel HP80 in sea water when full of air is -8.5# and -2.5# when empty. The buoyancy of an AL80 is -2# full and +4 lbs empty. If you keep everything else constant (BC, suit, etc.), then theoretically you should need 6.5# less when you switch from your Al80 to the steel HP80. This is the difference in the buoyancy of these cylinders when empty (4 - -2.5)

 

[WD8CDH]

Personally, The only time that I absolutly wouldn't use a steel tank (or any tank) would be if the tank (or tanks) made me negative with no weight. Other than that, I tend to prefer aluminum for 50cuft and under and steel for over 50 cuft.

I really wish we could get 300bar steel tanks here in the US. I especially like the 300 bar 7 liter tanks. About 80 cubic feet in the size of a steel LP45 with only a slight increase in weight.

 

[ScubaMarc]

Steel tanks last forever, if you care for them properly, and make sure no water gets inside of them during the refill process (such as on a boat).

Only if fills were only done by you and on your own compressor, you can say you this. No matter how well you take care of your tanks, fills are not always what you expect.