Steel vs Ally Tank?

[gee13]

Hi guys

I know this has probably been discussed before and if there's a thread on it please send a link, but im looking at main differences, pros and cons. I've been given different opinions and undecided. Any thoughts would be good. I have dived them both and am steering toward steel as I have tended to go upward as ally tank gets to 50 bar.

I dive with a 5mm semi dry and use 9kg (19 lb) weight on a standard bc (not wings on backplate), To be honest havent done full weight check but I can decend easy and swim up with my rig on using steel. A couple of times I have floated up using allys at the end of dive, I may have had air trapped in the bc, not sure. I would rather not have to add more weight by going allys. Im still only on less than 20 dives so still learning.

Any info would be appreciated. Thanks.

 

[PerroneFord]

Aluminum offers zero advantage in this instance.

 

[smoothfin]

i've got both steel and aluminum tanks, and my primary motivator for getting the aluminums was the price difference.

 

[charlesml3]

This argument has been beaten to death here. It's funny how religeous people will get over this. One guy even said he dove steel. Period.

I don't understand why anyone would need to be that stringent. I keep a little hand-written chart in the front of my dive log book with various tank sizes (80 and 100 cu ft), composition (Aluminum or Steel) and my two wetsuits (full and shorty). The column over is "Weight needed." I just look up what size, composition and suit and put on that much weight. I don't think it needs to be any more difficult than that.

It really pays to be flexible and be able to adapt to the circumstances. You never know when you're going to get to the dive boat early one morning to find that all of the 80's or all of the steel tanks are on other boats.

-Charles

 

[rstofer]

At the end of a dive, an Aluminum 80 might be 4# positive and an HP 100 (steel) might be 2# negative. That difference, 6#, is the additional weight you must carry somewhere when using the Al 80. Usually on a weight belt/harness but sometimes in trim pockets or as tank weights.

Oddly, the HP 100 will be lighter than the Luxfer S80 by about 2#. This is only important as you trudge across the beach and the difference is lost because the HP 100 will carry 2# more air. But 2# of air can be useful.

There might be warm water conditions where a wetsuit isn't required and only 4# is necessary when using an Al 80. In this case, the highly negative feature of a steel tank isn't important. Singapore, Malaysia, Thailand, the Maldives: I dove all of these in a Lycra skin with an Al 80 and perhaps 6# of lead. I probably only needed 4#.

Richard

 

[spectrum]

Hi guys

I know this has probably been discussed before and if there's a thread on it please send a link, but im looking at main differences, pros and cons. I've been given different opinions and undecided. Any thoughts would be good. I have dived them both and am steering toward steel as I have tended to go upward as ally tank gets to 50 bar.

I dive with a 5mm semi dry and use 9kg (19 lb) weight on a standard bc (not wings on backplate), To be honest havent done full weight check but I can decend easy and swim up with my rig on using steel. A couple of times I have floated up using allys at the end of dive, I may have had air trapped in the bc, not sure. I would rather not have to add more weight by going allys. Im still only on less than 20 dives so still learning.

Any info would be appreciated. Thanks.

The reason you rise at the end of the Dive is the loss of weight as you consume the cylinder contents. Cylinder material is irrelevant. You are under weighted, plain and simple. (or not effectively venting your BC)

Remember to set your weight so that you bob vertically at eye level at the end of your dive with an empty BC, an average breath, your feet still (crossed) and about 500 PSI in your cylinder. A deep breath should get your mask out of the water and a deep exhale should sink your mask. Do all of this while breathing from your regulator. The end of the dive is the defining moment for your weight requirement and you want just enough to let you stay down in the shallows with a light cylinder.

You can make the same test pre-dive with a full cylinder and add 5 pounds to compensate for the buoyancy gain you will experience as you breathe the tank down. Be sure to repeat at the end since you are apt to have some stowaway buoyancy (trapped air) in your gear early in the dive. You are safer being two pounds heavy than 2 pounds light.

Since you are wearing moderate neoprene a steel cylinder can offer other advantages SCUBA Knowtes, The Evil Aluminum 80SCUBA Knowtes, The Evil Aluminum 80

Pete

 

[gee13]

At the end of a dive, an Aluminum 80 might be 4# positive and an HP 100 (steel) might be 2# negative. That difference, 6#, is the additional weight you must carry somewhere when using the Al 80. Usually on a weight belt/harness but sometimes in trim pockets or as tank weights.

Oddly, the HP 100 will be lighter than the Luxfer S80 by about 2#. This is only important as you trudge across the beach and the difference is lost because the HP 100 will carry 2# more air. But 2# of air can be useful.

There might be warm water conditions where a wetsuit isn't required and only 4# is necessary when using an Al 80. In this case, the highly negative feature of a steel tank isn't important. Singapore, Malaysia, Thailand, the Maldives: I dove all of these in a Lycra skin with an Al 80 and perhaps 6# of lead. I probably only needed 4#.

Richard

Hi Richard

Don't mean to sound ignorant here but what do you mean by '#'

Thanks

 

[tgsmith]

Pounds. The "#" symbol is called the pound symbol over here in the U.S. so you will sometimes see us use that instead of be so hardworking to write "lbs" or even "pounds." So I guess kg for you. 1kg=2.2lbs.

 

[gee13]

Thanks for the clarification. Interesting you say the difference is 6# for the difference in weight between ally and steel as I did an ally dive with and extra 3kg - 6# and worked out to be perfect balance.

Problem is...from what I hear from more experienced divers is for more weight I need to compensate my bouyancy much more with air in bc going deeper which is not the best thing. They say i need to lose a lot more weight than what im carrying at the moment - 12 # with steel.

I admit havent done a weight test but one question I have for all you experienced divers is - Is it better to loose more weight and dive lighter? with better bouyancy control? Or does it not matter if you put on an extra 3 pounds to limit going up too quick on ascent?

Thanks again

 

[rstofer]

One school of thought: if you are carrying too much weight, you will need to use more air in your BC to control buoyancy. This air changes volume with changes in depth and the resulting change in buoyancy requires constant fiddling. Consider excess weight like an amplifier. The more you change depth, the more you need to fiddle with your BC.

Most people suggest you set your initial buoyancy so that you float eyeball high with an empty BC and an empty tank. This has been the standard approach for many years.

Tobin, at Deep Sea Supply, has a different approach and it may apply more specifically to 7mm wetsuits. He suggests eyeball high with an empty BC and a full tank. In the case of an HP 100, this will result in the diver carrying 8# less lead assuming the tank ever gets completely empty.

So, how do you control your ascent since you are 8# more buoyant (or 8# less negative)? The thought is that a) the tank is never really empty or you wouldn't be making a safety stop and b) wetsuits compress at depth and they lose buoyancy. They don't necessarily decompress quickly and they are less buoyant at the end of the dive for a given depth. Besides, wetsuits lose a lot of buoyancy between the surface and 15'. So, it ought to work.

I haven't reached this point yet but I'm getting there. I'm not sure about being able to dive in the top 15' after the safety stop without bobbing up. It's suppose to work. We'll see.

With the DSS method, you are not negative at the start of the dive. You will not be able to vent your BC and sink like a stone. Tobin suggested kicking up and dropping back down. This is his recommended technique for diving in kelp rather than inverting and swimming down. The act of inverting could result in entanglement.

Maybe somewhere in the middle. I won't drop the entire 8# but I might try to drop 6# or so.

Richard