Dual steel 72's bouyancy

[Arcaporale]

I have gotten hold of some old steel 72's with 3/4" necks rated to 2250psi (2400psi w/ the + rating). I want to dual them up using Highland Millworks tank bands and a Halcyon DIN manifold.

That being said, my question is how much weight should I be using with them while wearing a 6 lb. backplate for diving in saltwater with a drysuit?

I allready know that my bouyancy is perfect while using one tank and 12 lbs. + the 6 lb. backplate.

My second question is, what would be a good size BC to wear with the duals, the Halcyon Exlporer 55 lb. or 40 lb? Could I even use an Eclipse 40 lb. BC with duals?

My gut tells me I should be using an Explorer 40 lb. wing with about 6 lbs. of lead in addition the 6 lbs. from the backplate.

 

[TSandM]

You don't say what kind of single tank you were using.

I was diving an LP 95, using a 5 lb SS backplate, 3 lbs on the cambands, and 18 pounds on my waist, for a total of 26 lbs. When I went to the doubled 72s, I switched to an Al backplate to get my head out of the sand, and needed 18 pounds on my waist. So I effectively dropped seven pounds.

I have heard that the buoyancy on the old 72s can vary, so I'd suggest the first dive with the doubled tanks be a shallow one.

 

[ScubaJewel]

Both My husband and I dive similar units, Buoyancy characteristics still depend upon who made the tanks but you should need less weight and that's for sure.

Are the tanks similar manufacture both height and date?

 

[DA Aquamaster]

I use 8 lbs less weight with double steel 72's than I do with double AL80's. The cool thing is that the total weight including tanks and lead is about 16 lbs lighter with steel 72's than double Al 80's.

In short, the "average" steel 72 is about 4 lbs less bouyant when empty than an AL 80 and is neutral to maybe 1 pound negative when empty.

They do vary slightly by manufacturer and date/era and possibly moon phase on the day they were pressed but most do not stray too far from those numbers. Of the 20 or so that I have owned only 1 was radically different than that so the odds are pretty good that yours will be in the ballpark.

I have used mine with both a 55 lb pound Explorer wing and with a 40 lb Rec wing and both work fine. But the 40 lb wing is adequate even in cold water diving as the tanks are not excessively negative. They are a workable set of doubles for a wet suit diver along with AL 80's and there are not many other tanks that I am comfortable adding to that list.

 

[Arcaporale]

They are both the same dimensions but have different manufacturing dates. I am positive that they will work together. I just need to get the hydro done on both of them.

Another question is, should I get them painted? I hear it's not good to have painted tanks banded together.

 

[Arcaporale]

So if I dive a single AL 80 with 18 lbs. of weight, then I think I should use about 8 lbs. of lead in addition to the SS backplate. Obviously I can't know for sure untill I actually dive the rig, but I want to get a ballpark idea of what I should be at so I'm not over or under weighted on my first dive with it.

Another question is how much will tank's bouyancy change if I overfill the tank to 3000psi or so?

 

[SeanQ]

Another question is, should I get them painted? I hear it's not good to have painted tanks banded together.

How are they coated at the moment? I have a similar pair of 2475psi (2250+10%) Norris 72's (still singles) that are galvanized.

 

[Arcaporale]

They are both painted. One has the paint peeling off and some white oxidation/corrosion on the outside, however it is very light, nothing to make the tank unusable, and nothing on the inside. The other is in really good shape, not a bit of corrosion or anything just needs a hydro.

 

[Arcaporale]

Hey Everyone, Thanks For The Input, I Guess The Best Way To Find Out My Proper Weighting Is Trial And Error, But I Think I Have A Pretty Good Idea Where To Start.

 

[FredT]

They are both the same dimensions but have different manufacturing dates. I am positive that they will work together. I just need to get the hydro done on both of them.

Another question is, should I get them painted? I hear it's not good to have painted tanks banded together.

Leave ALL 72s unpainted! The tank's galvanizing works a lot better that way.

FT