Why doubles AL40s instead of AL80 or HP80?

[Jimmer]

I own a set of double Faber 45's. They sit very low to my back, are better balanced than a single, and in certain circumstances they were the right tanks for the job. One example of that was an ice dive I did last winter. Max depth of 20 feet, bu 14 inches of ice overhead. I didn't need the volume of my double 72, but I wanted the redundancy of double first stages, in the event of a freeze up or major freeflow.

As an aside, they are just plain fun to play around with, and were great to do shallow training dives for my intro to tech class, where I needed to be profficient in valve shut downs.

 

[mike_s]

Question for the tech doubles divers. If the function of doubles is to increase the volume of available air for longer dive time, then why dive doubles AL40s instead of a single AL80 or HP80? Same volume and alot simpler & less expensive setup. I can understand doubles AL63 rather than one HP120 or 130 since those tanks are so long and heavy for a short person.

Does this seem like overkill just to brag that "See my gear, I am a tech diver" ? I observed this yesterday as I watched a PADI recreational Rescue class in 30 ft of water, the instructor (a short lady decked out to the max in all of her tech gear) was diving double 40's. I will add that the tanks were Nitrox 32%.

Can anyone share any good explanations?

the main realist benifit to having double 40's (over a single 80) is redundant first stages, redundant valves and an isolator manifold.

If one of the regulator first stage froze up, an or free flowed, or an o-ring blew, you could turn it off at the valve and use the other regulator and still have access to any air/gas left in both tanks. If one of the valves leaked, blew-out, etc, you could turn off the isolator and still have the air/gas in the remaining tank.


Maybe she was decked out just to have the toys.... but maybe she had really good air consumption and just didn't need bigger tanks, yet still wanted the above redundancy. (I know some women divers that have much better air consumption than most men).

 

[captain]

Maybe she learned what us vintage divers learned years ago. Small double are streamlined and trim out better. Of course we didn't bother with two regulators or isolation manifolds.

 

[texdiveguy]

I am thinking of giving a set of Al19's a try.

 

[Nemrod]

Let's see, maybe she only has a doubles wing?

Maybe she agrees with Nemrod, standard doubles plates and single tanks are a poor match.

Maybe she likes the way they feel and trim and balance.

Maybe she likes the fact that twin 40s hold a true 80 cf instead of 77cf?

Maybe she like the fact that equippped with dual regs, bands and manifold the rig would probably be neutral or negative when empty instead of four pounds bouyant like a single standard 80?

I also have double 40s and double 50s and sooner or later a triple 30/40 but I am not into all of the redundancy but I do like the balance, trim, feel, streamlining. Nobody mistakes me for a tech diver, I am past that. Don't care what they think anyways.


Hey if you just run 100% O2 and just major skip breath could you do the Doria and not need to decompress?
N

 

[HowardE]

Double Steel 55's are great btw. They have them at Pirate's Cove in the DR.

 

[TxIceDiver]

I have seen this configuration before and wondered why 2 small tanks instead of a larger one. With only 80cuft of gas, you won't be going all that deep or staying all that long.
We were ice diving at the time and I figured out that it was purely for redundancy, as the regulators can freeze up and free flow. if that occurs, then you can shutdown one of them and switch to the other. In ice diving you don't usually need a whole bunch of gas, as the dives are pretty short. And 2 40's gives you the redundancy without all the weight. (one guy dove with double steel 108's, man that was a heavy rig)

Another configuration that works well for the ice is to use and H-valve with 2 regulators. (this is what I use)