Independent doubles

[Thalassamania]

Many of your question are addressed in:

Pyle, R.L. 1992. The Twilight Zone. AquaCorps: Mix. 3(1):19; and 3(1):17-21.

and

Sharkey, P. and . R.L. Pyle. 1993. The Twilight Zone: The potential, problems, and theory behind using mixed gas, surface based scuba for research diving between 200 and 500 feet. In: L.B. Cahoon (Ed.) Diving for Science...1992. Proceedings of the American Academy of Underwater Sciences Twelfth Annual Scientific Diving Symposium, American Academy of Underwater Sciences, Costa Mesa, CA. pp. 173-187.

 

[DevonDiver]

How deep are you planning on diving? I would recommend talking to a Tech Instructor that dives sidemount. Diving with multiple tanks/gasses and doing switches is not normal recreational diving.

sidemount? do you mean stages?

Gas switching, between different gas mixes with varying O2 contents is very definitely entering into the world of tech diving.... even if those gas mixes were all 'recreational' sub-40% nitrox mixes.

There is nothing within recreational nitrox training that qualifies or prepares you to switch gases during the dive. This is a big potential killer.

The old DSAT Tec1 course used to aim/qualify specifically for this. There are some new dangers involved when you start multi-level, multi-gas diving...and it is worth getting some appropriate training to achieve safety and proper awareness of those issues.

 

[DevonDiver]

Here is a picture of Richard Pyles old rig where he dove with different mixes back mounted. You can see the degree of complexity involved.

This rig was used by Pyle. He knew what he was doing with it. He developed it for a particular reason and with specific requirements. It's far from ideal, in every respect, for a less experienced doubles diver. IMHO, it is a potential death-trap....even without the back-mounted O2 and Trimix.

There is absolutely no need for the twin Air2 contraptions. You've got a regulator to hand-off to a buddy...and plenty of gas if they have a failure. There's no need for 4 regulators on a set of doubles.

All you need, on each post, for a set of indie tanks is:

1x Regulator.
1x SPG
1x LPI (1 or 2 depending on single/double bladder or if drysuit is used).

 

[rjack321]

All of you said much better, what I was thinking.
However the question was to extend time, not do deco?
i.e. I dive to x untill ndl is reached then ascend to a shallower depth where a hot nitrox mix say 36is the appropriate mix. At a minimum a 2 gas computer would be required and all the problems still remain, as well as a lack of understanding of multi-level profiles with an imperfect mix for one of them on open circuit.
Maybe a ccr is in order? lol
Eric

Depending on what you've done before on the deeper gas and what that gas was (air?), you'll have a couple of minutes before you hit the NDL on the EAN36. Certainly not worth bringing an 11L tank of it, screwing the pooch on the bottom & dying.

Get some deco training, these questions are addressed there.

 

[deepdvr1]

sidemount? do you mean stages?

Gas switching, between different gas mixes with varying O2 contents is very definitely entering into the world of tech diving.... even if those gas mixes were all 'recreational' sub-40% nitrox mixes.

There is nothing within recreational nitrox training that qualifies or prepares you to switch gases during the dive. This is a big potential killer.

The old DSAT Tec1 course used to aim/qualify specifically for this. There are some new dangers involved when you start multi-level, multi-gas diving...and it is worth getting some appropriate training to achieve safety and proper awareness of those issues.

I ment sidemount, but only for the gear configuration. Not the gas mixes and techniques used. Thats what I pictured in my head when I read the original post.

 

[kanonfodr]

Im trying to see why trim wont be affected with one tank more depleted. Then it occurred to me that you were banding them together in the plan. I was thinking sidemount I suppose. It was also before my coffee was done perking. Alot of divers have perished breathing the wrong mix at depth. I dont think the extra BT is worth it.

Trim won't be affected much because gas in the wing will move through it to stabilize itself, or you can give it a hand by rolling up on the light side of your body and letting gas get in the high part of the wing. Look at a technical diver carrying a few extra bottles on the left side: the left side of their wing is carrying more gas so it rises higher than the right side, the gas counteracts the weight of the bottles.

Peace,
Greg

 

[Thalassamania]

Having two different mixes in tanks you can't see strikes me as a really bad idea. If you're going to go into deco, get the training and sling your deco gas so you and your buddy can verify the mix and depth before you breath it.

This rig was used by Pyle. He knew what he was doing with it. He developed it for a particular reason and with specific requirements. It's far from ideal, in every respect, for a less experienced doubles diver. IMHO, it is a potential death-trap....even without the back-mounted O2 and Trimix.

There is absolutely no need for the twin Air2 contraptions. You've got a regulator to hand-off to a buddy...and plenty of gas if they have a failure. There's no need for 4 regulators on a set of doubles.

All you need, on each post, for a set of indie tanks is:

1x Regulator.
1x SPG
1x LPI (1 or 2 depending on single/double bladder or if drysuit is used).

We hold different opinions. But then, I actually dove a similar version of the rig with Rich, who was diving that same rig, and you did not.

I recommend that anyone who wants to know exactly why Rich designed his rig the way that he did, read his articles and correspond with people who have actually used it.

 

[DaleC]

When I do as many deep dives as Richard Pyle I'll tell him what a dumb set up that is but until then I'll respectfully abstain from critism and just try to understand it.

I posted the image to show the OP how complex a rig using different mixes would be (if one could not bailout from one mix to the other). It was meant to be a sober second thought not a recommendation.

But who sets up all these rules about what recreational divers do and don't do anyways. What courses did Richard do to gain the experience he had to dive that rig? My bet is he just thought it up to serve his needs.

 

[Thalassamania]

In the paper quoted above, Sharkey does a failure mode analysis on Pyle's rig similar to the ones that he published on several deep submersibles.

 

[stairman]

Ive dove many times with backmounted steel 98's and an aluminum 80 slung with no off kiltering affects. Now that Im sidemounting with twin 85's, I notice quite a difference in balance as one tank gets lower which is why I switch regs about every 300 psi. I confused the OP with carrying the tanks in this fashion. Again IMO too dangerous to backgas 2 mixes unless your real careful about it. If your already doubled for backmount having an exotic mix in a stage is safer and less prone to a mistake.