What tank: AL80 or steel?

[SteveR1952]

But think that your wetsuit is not offering any buoyancy when your are at depth I am not talking at the surface where your wetsuit provides lift. So what is going to help you up. With an alum you will have positive buoyancy that will provide lift just like adding air to your wing. A steel will offer nothing and you will have to swim it up. Check with the DIR guys they recommend aluminum with wetsuit steel with drysuit for singles so that you always have redundant buoyancy.

The only issue I see with this logic is that the AL80 will require around 5# of lead to keep the diver from being too bouyant at the safety stop. A steel tank would require less lead so would actually be easier to maintain bouyancy at all depths and would be easier to get around out of the water.

I believe a properly weighted diver would need to swim up to some degree from any depth lower than 5-10 feet from the surface. Of course if you are way over-weighted it will be harder to get going but as you rise your bouyancy will be less negative.

I for one would not want to rely on a tank to lift me up to the surface...on the contrary..I want to be in full control of my ascent. That requires a diver be properly weighted for the dive..regardless of the tank used.

 

[Gombessa]

The only issue I see with this logic is that the AL80 will require around 5# of lead to keep the diver from being too bouyant at the safety stop.

Note that this is only relative to a steel tank that is about -1lb when empty, there are several exceptions (notably the MPs and some HPs).

I believe a properly weighted diver would need to swim up to some degree from any depth lower than 5-10 feet from the surface.

This is only true at the beginning of the dive, and even then I think "swim up" should probably be broadened to include lift afforded by the wing and lung capacity.

At the end of the dive, a properly weighted diver should be neutrally buoyant at ~15ft with a nearly empty tank and no gas in the wing; as such they should not "need" to swim up from that depth to the surface, they can initiate and halt an ascent at any point using only lung capacity, with no swimming required.

 

[SteveC]

But think that your wetsuit is not offering any buoyancy when your are at depth I am not talking at the surface where your wetsuit provides lift. So what is going to help you up. With an alum you will have positive buoyancy that will provide lift just like adding air to your wing. A steel will offer nothing and you will have to swim it up. Check with the DIR guys they recommend aluminum with wetsuit steel with drysuit for singles so that you always have redundant buoyancy.

While it’s true that weight on your tank verses weight on your belt changes your ditch able weight options, that’s as far as it goes. The problem that I am trying to address here is the point that steel tanks will become just as buoyant as aluminum of the same cubic feet. I think that where most people get confused is when they hear that the steel tank is –1 lb at the end of the dive they assume that they won’t be more buoyant. This is not true because the tank was –6 lb at the beginning of the dive, so they are still the same 5 lb more buoyant and the end of the dive. So if you’re diving a steel tank and your barely negative at the beginning of the dive you will still have trouble with your safety stop at the end of the dive.
So if you need more ditch able weight, the alum tank will allow you to put more lead on your belt, and if you want less ditch able weight the steel will allow you to take some off your belt, but if you breath 5 lb of air you will always have to content with being 5 lb more buoyant at the end of the dive. This is true whether your tank is Alum, Steel, Titanium or any other material.

 

[mpgunner]

I dive all steel. The only way to go and lower your weight.

 

[Jax]

Thank you, guys, for these extremely informative and well-debated postings!

 

[RonFrank]

Alum tanks have some characteristics that make the nice. They are (in general) lighter than steel but the XScubs Steel HP 100's are about the same weight as the AL80's. Alum does not corrode easily vs. steel which can get flash rust, and pit. They are also cheap, and most rec divers find that the AL80 holds enough air for most rec dives.

The downside of Alum is the buoyancy characteristics are not as good being 2~3lbs negative full, and 3~4lbs positive empty. You can purchase neutrally buoyant AL tanks which are a couple lbs negative in the water when empty. They cost more than standard AL tanks.

The poster that indicated that AL does not last is wrong. They last fine, but there were some of a particular type of Alum 6351-T6 and 6576 in the late 70's and 80's that DOT condemned. Alum tanks can outlast steel as steel is a more corrosive metal.

I have a couple of AL80's, and for local diving where I live, they work fine. Most of the world dives on AL80's, so while steel maybe my first choice, I can not justify spending $360 a tank (new) for steel to do the diving I do. They would make very little difference to me in the water even if I would LOVE to find some Steel 100's on the cheap used.

If the tanks you are looking at have an initial hydro date in the 2000's or better yet current hydro and VIP you *should* be fine. The last batch of bad Alum tanks were Luxfer made in 1988 I believe, and they would not be in current hydro. ALL Catalina tanks are good, regardless of the date as they used 6061-T6 alum (good alum).

If you attached 3lbs of lead to the CAM band when using AL80's you would basically have a neutral AL80, and that is a HECK of a lot cheap vs. Steel. If you NEED more air (new divers often do, but grow out of it), than the Steel 100's are great. I prefer larger volume tanks when diving flat deep profiles in the 80'+ range using Nitrox.

I'd say buy the alum. If you find a good deal on steal in the future, you can always sell them. If you go tech, they make great stage bottles. I know very few tech divers that don't own AL80's on top of their steel doubles. I also know a few tech divers that dive AL80's in a double configuration. Sure not the best buoyancy characteristics, but they work fine.