Selection of new Alum 80

[tinman]

I will be purchasing two new Aluminium 80 tanks in the next couple of weeks. I will normally be diving with a single tank but might consider diving as a double at some future date. Would this affect the variety of 80 I'd buy now or only the future purchase of values, etc. Any features besides colour, rubber boot to be considering? They will be yoke not DIN...

 

[Goldminer]

Originally posted by tinman
I will be purchasing two new Aluminium 80 tanks in the next couple of weeks. I will normally be diving with a single tank but might consider diving as a double at some future date. Would this affect the variety of 80 I'd buy now or only the future purchase of values, etc. Any features besides colour, rubber boot to be considering? They will be yoke not DIN...

I am in the same position as you, thinking about a tank purchase that may get twinned in the future. Although I have never been on a dive with a twin set the advice I have heard is that aluminum tanks don't twin well (see caveat below). Two empty conventional AL 80's are about +8 lbs buoyant. Whereas 2 steel tanks, depending on size and manufacturer, would be neutral to slightly negative. You would need to carry an extra 8 to 9 lbs of weight on surface, which, in addition to the twin set, may be a lot of weight (depending on what other gear you dive with). The manifold, bands and back plate would provide much of this weight but with steel tanks the weight could come off of the belt.

Catalina makes compact, neutrally-bouyant Al 60's, 80's and 100's. I don't know what they cost but they are probably a lot more than the standard Al 80 as they have a working pressure of 3,300 psi. You might want to consider LP steel tanks. I will be.

I do dive cold, fresh water though and have significant exposure protection. I need ballast weight. Your situation may be different. Get expert advice on your situation.

 

[nickjb]

Not sure what the situation is over the pond but in Europe DIN is getting more and more popular. If you are buying new it should be easy to get A-clamp valves that have a removable insert for possible conversion to DIN at a later date.

 

[C_C]

When I first started diving doubles, I was diving wet and chose to double up 2 AL 80's.

Steel cylinders would have been too heavy with no redundant bouyancy.

If you were to double them up, my suggestion would be to find two cylinders that are REALLY close in serial number from the same manufacturer. Your LDS may purchase their cylinders in lots which will give you a better chance of finding two VERY similar cylinders.

All cylinders are not created equal. The manufacturing process allows discrepencies within certain defined limits that could make it difficult to match cylinders.

Catalina cylinders permits a certain amount of "bowing" to the cylinder. Banana shape if you will. It does not affect the "quality or usability" of the cylinder, but will make it difficult to double up.

Luxfer has similar specifications, as does all steel manufacturers.

As for color and boots, I have two different color cylinders...which always helps my buddies find me at depth and I do not use boots on any of my doubles.

As for the weight swing...that you will experience with steel or aluminum...I use an 8 lb. V weight that I made similar to the ones that Dive Rite sells that fits between the bolts on the bands.

Good luck,

Hope this helps.

C_C

 

[tinman]

Sorry to confuse things...I don't see myself diving "doubles" for some time to come, but who knows. I will always go to a dive site with two tanks...it seems such a waste to leave a site with only one dive - I came I saw I dove....

That said, I agree that adding weight to AL80s sounds like a better solution since steel tanks are some damn heavy to lug around...

 

[gentlegiant]

Tinman,

There is a bit of a problem with your logic about buying tanks. AL80's are actually heavier on land than steel 80's. A typical AL80 empty weighs 31lbs and a HP steel 80 weighs 28.6. For the same tanks, when empty, the AL tank is positive 4.4lbs in saltwater and the steel is negative 2.5lbs in saltwater. The AL100 is actually 7lbs heavier than a HP steel 100 (I have not had the time to look up the numbers for LP steel tanks but I think they might even be lighter). Steel tanks are a bit more expensive than aluminum tanks, but for me the advantages of being able to get rid of extra lead weights and the better balance of the steel tanks outweigh the price difference.

 

[Marlinspike]

For what its worth, I own two neutrally bouyant aluminum 80s made by Luxfer and available through Sea Quest dealers. I bought them with yoke valves but will have these cylinders switched to DIN soon also. They go by Luxfer NB 80.

Service pressure is 3300 psi.
They are great .

Also, GUE/DIR recomends double aluminium tanks (cylinders, if you like) for ocean diving in a wetsuit.

Hope this helps,
Marlinspike

 

[tinman]

CB: I stand corrected...misinformation from a dive buddy. Why does DUI recommend alum I wonder...

 

[gentlegiant]

I think I have figured out why DIR/GUE recommends AL tanks for wetsuit divers. Let's start by looking at the typical DIR/GUE BP/wing configuration, typically the BP is steel and is about 6 pounds negative. Now we take that and add a single tank adapter, unless you are diving doubles which is even nore negative weight, which weighs a couple more pounds. Throw a steel tank on top of this and you have a configuration that is 8-14 pounds negative for a single tank setup.

For a diver in a wetsuit this much negative weight could lead to you now diving with no extra lead weights and possibly still being negative. I think the main concern is that a wetsuit diver in this situation who has a BC failure would not have a way to counteract this negative bouancy and that would be a problem. this would not be as big an issue for a drysuit diver because they can always inflate the drysuit to get positive.

I hope I have gotten this right, at least in theory. My personal recommendation is this:
No matter what tank you choose to buy after it comes in spend some time with it and your gear setup in confined water making sure your weighting is correct
I try to do some pool practice each time I make a change to my gear configuration so I do not have any nasty surprises on my next "real" dive.

 

[tinman]

I'm a confirmed wet & semiwetsuit diver so I was very interested in your analysis of DIR's thoughts. Your conclusions make sense to me. I think the other reason I will stick with Alum for now is that virtually all rentals are Alum that I've encountered (any different in the Caribbean or Southern USA?) and I would prefer to be configured and comfortable with Alum 80s. Tx again for your cogent review of the pros/cons of the two materials.