Why doubles AL40s instead of AL80 or HP80?

mselenaous · Dec 20, 2008

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?

Lone Frogman · Dec 20, 2008

Redundent air supply.

mselenaous · Dec 20, 2008

She had that too (a 13cf pony).

Blackwood · Dec 20, 2008

mselenaous:
She had that too (a 13cf pony).

maybe when diving with students she feels the need for extra redundancy. In this case, she has (presumably ) three independent gas supplies.

Note that you won't see "tech dives" on such a configuration. Bluntly put, they don't hold enough gas. However, it's adequate for shallow training dives, and isn't hard on the back.

jeckyll · Dec 20, 2008

mselenaous:
She had that too (a 13cf pony).

How about "there is no accounting for some people"?

Perhaps they trim out really nice and she has the lung capacity of a sparrow? Perhaps she really likes a 'different' setup.

Or maybe her dives are only 15 minutes long (at 30 ft).

Maybe ask her next time you see her and let us know

caseybird · Dec 20, 2008

mselenaous:
:

Does this seem like overkill just to brag that "See my gear, I am a tech diver" ?

Can anyone share any good explanations?

Let's see, 2 40's ride much lower on the back than 1 80, putting her center of gravity much lower, thus reducing any tendency to roll onto her back.
Much lower profile for wreck or cave penetration. (remember, you said she was wearing a tech configuration).
Remember as an instructor with students, she has NO buddy, therefore MUST carry her own back-up air supply, Thus:
Redundant air system without a pony bottle or stage tank, no assymetrical load or shifting stage tank. No stage tank obstructing her left arm. A lot less weight (38 lbs. +-) than dual 80's.
Twin 40's have plenty of air for relatively short shallow training dives.
Less weight to haul around on shore than twin 72's or 80's.

Seems like a good idea.

don Francisco · Dec 20, 2008

If I remember the old Sea Hunt episodes correctly, Nelson dove doubles and the bad guys dove singles.

Her decison might have been based the shape of the air supply. Two Al40's would be a shorter rig than an AL80, and the woman might have preferred that setup. If you're really curious, ask her next rime you see her.

Meng_Tze · Dec 20, 2008

Because it made her look good and interesting! That is the only reason I can think of in the scenario described: a shallow open water training session.

micklock · Dec 20, 2008

I love diving with my twin steel 40s. They sit close to my back, very balanced, -3.3lbs each empty and I don't have to change my reg set up or hose routing when I use my larger twin tanks.

NudeDiver · Dec 20, 2008

It's interesting that the first assumption that some people make is something generally negative - "ooh, look at me - tech diver" or "wants to look different/interesting" (posts 1, 5 and 8).

Fortunately, the info provided by several of the other posts provide some good theories. I particularly like the one about changing the center of mass. I know I often feel like my face is being shoved down in the water - changing my center of mass has some appeal. I realize that there are other ways to do this - but my point in mentioning it here is that several of the theories here seem like good ones.

I like the advice to just ask her best though. Seems like a reasonable thing to do

Why doubles AL40s instead of AL80 or HP80?

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mselenaous

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