Single vs. double tanks

[ColdH20diving]

I met a diver recently who was diving with double 72's. He told me he used to dive with a larger single tank, but found that the shorter 72's offered better balance and he was able to maintain an almost level position as opposed to using a larger single tank. I like diving my single 112 but have considered going to a smaller set of doubles especially if it helped maintain a level position underwater. I've always heard that double's tend to increase your drag and take some getting used to.

 

[Don Burke]

ColdH20diving once bubbled... I met a diver recently who was diving with double 72's. He told me he used to dive with a larger single tank, but found that the shorter 72's offered better balance and he was able to maintain an almost level position as opposed to using a larger single tank. I like diving my single 112 but have considered going to a smaller set of doubles especially if it helped maintain a level position underwater. I've always heard that double's tend to increase your drag and take some getting used to.

I've got two sets of 72s and I really like them. It seems they put the changing weight of the gas in my tanks right at the wing so I find it easier to stay level.

I dive with some guys who use 131s, and I can stay with them with the 72s.

Yes, there is a little more drag. It doesn't seem to be a big deal.

 

[Dryglove]

I have two sets of steel dbl 72's. I really like them and sold my larger single tanks after i dove my first set a few times. I set mine up with a isolation manifold so i have two first stages with each first stage having its own second stage. I have a LP hose from each first stage for my wing and drysuit. So i have redundancy on my regs plus my my ability to make it to the surface in a nice controlled manner should one of my first stages malfunction or my wing takes a dump. The down side is that i have to pay twice as much for fills.

 

[ERP]

I have a set of double LP80's and I dive HP120's as singles.

I think the 80's are easier to trim out, but I can get and stay horizontal with either. The redundancy of the doubles is nice and the weight difference is managable.

 

[DA Aquamaster]

A pair of steel 72's offer 142 cu ft when filled to 2475 psi and still offer 130 cu ft at 2250 psi. At a little over 60 lbs total with valves a pair of steel 72's are also very competetive from a weight standpoint when compared to a single tank of comparable capacity and are only slightly heavier than some 120 cu ft singles.

I use travel bands with mine and configure them as independent doubles. On a short single tank dive I, in effect, have a really large pony bottle and only have to change out one tank at the end of the dive.

On longer dives I still have the air capacity of a 130-140 cu ft single tank with the added benefit of the redundancy of a doubles setup. Air management is slightly more complicated than with manifolded doubles, but the system is far more flexible and more ammenable to traveling and use with rental tanks. Keeping 20 individual 72's offer a lot more flexibility then setting them up as manifolded doubles given that not all of the 3 divers in the family dives doubles. They are also a whole lot easier to transport.

 

[Dryglove]

DA Aquamaster once bubbled...
A pair of steel 72's offer 142 cu ft when filled to 2475 psi and still offer 130 cu ft at 2250 psi. At a little over 60 lbs total with valves a pair of steel 72's are also very competetive from a weight standpoint

Would you happen to know what the buoyancy characteristics of a steel 72 ? I asked five people and got five different answers but no one seemed to know for sure

 

[Don Burke]

lal7176 once bubbled... Would you happen to know what the buoyancy characteristics of a steel 72 ? I asked five people and got five different answers but no one seemed to know for sure

I take twelve pounds of weight off when I switch from double AL80s to double steel 72s.

 

[Compressor]

Make sure you have a BC or Wing that has enough lift for the double Steel 72s.

 

[DA Aquamaster]

You'll need a wing or BC with a minimum of 45 lbs of lift for warm water diving with double 72's and 75 lbs of lift is better for cold water diving where you are using more lead for the heavier exposure suit.

I have not dove an AL 80 in several years but I needed to add about 4 lbs of weight to maintain neutral bouyancy when switching to a single AL 80 from a single steel 72.

 

[roakey]

DA Aquamaster once bubbled...
You'll need a wing or BC with a minimum of 45 lbs of lift for warm water diving with double 72's and 75 lbs of lift is better for cold water diving where you are using more lead for the heavier exposure suit.

Oh my gawd, I thought we taught Archemedes principle in OW, I guess not.

You actually need LESS lift with steel 72s than with 80s, because they swing less (if you've correctly matched your cylinders to your exposure protection).

I can safely dive double 104s with a 45 pound lift wing (fresh water, which is the worst case), why on earth would you need 75 pounds of lift with double 72s?

Roak