Doubles vs. Pony/Spare Air

[ArcticDiver]

I posted this as part of another longer thread. But, I didn't want it to get lost in that discussion so I'm reposting here.

The basic question is: Why not just go to doubles instead of using a Pony/Spare Air?

At first glance it seems THE way to go. With doubles everything is out of the way on the diver's back. There is total redundancy. It leaves room for another gas bottle if the specific dive profile requires it. It gives a 100% redundant gas quantity backup. It solves the travel problem because the diver is only traveling with some regs, strapping and plumbing. The extra tank is furnished by the dive operator at the destination.

I have seen this done a couple times. The diver shows up with his regs and plumbing. The dive operator provides two AL80s. The diver takes about 15 minutes or so to set up the first time, less on subsequent tank changes. Seemed to work just fine. I should also explain that none of the dive trips I've seen this on have been "Tech Dive" trips or charter boats.

I'm getting ready to spend some money. But before I do I'd like to hear what folks more experienced in this have to say.

 

[2TH DIVR]

Independent doubles???
For the cost of a set of bands and a couple wrenches and the few extra minutes between dives to change out a tank. This would be the way to go. Gives you better balance than a pony.
If you are buying tanks , 3 80's will cost you the same as 2 80's + pony.
I hope you have a backplate and wing to build on.
Just my 2 cents

 

[eandiver]

The idea sounds really good but how many dive operators, other than the ones you have experence with, be agreeable to doing that?

 

[bluemagoo]

The idea sounds really good but how many dive operators, other than the ones you have experence with, be agreeable to doing that?

You're referring to shops letting out valveless tanks or unscrewing theirs? I've never come across a shop that'd do that; ones that do must be pretty rare birds. I'm curious as to packing things such as the manifold. I'd hate to allow BagSmasher Airlines have at 'em. Maybe use Pelican or hardside camera or gun cases?

 

[Jim Baldwin]

Artic,

I routinely dive doubles. PST 100 and 120's, and like the balance and backup regulator hanging under my neck as well as the additional gas. They are the ticket for deep, deco and wreck diving.

For most people they do not want to spend the extra for the dedicated tanks or training it takes to learn how to dive and properly use this setup. Things such as valve and isolator shutdowns and going to a backplate and wing. Let's don't even get into the long hose discussion.

When I am working with Advanced and Rescue students I show them pony bottles and the various ways to wear them. I advocate carrying one in the slung position. Using a pony requires almost no training. They can see the direct benefit of an independent air supply that can be carried on a standard BCD that they are used to or already own.

For those that want to get into tech diving I show them the backplate and wing and different gear configuration that is required and give them the name of a good tech instructor.

When I dive on vacation I dive with a long hose and bungeed short hose with my backplate and wing with a single tank adapter. I get questions from people who have never seen this type of setup.

Diving independent doubles takes additional training and good gas management similar to sidemount diving. For most it's just not practical.

If your goal is to do any of the TECH stuff then talk to an instructor prior to spending your money and buy the right setup for the type of diving that you anticiate doing. How big a tanks can you handle, drysuit, wing, backplate, twin regulators, dive reel lift bag, light, stage and deco bottles.

If you plan on doing regular recreational diving then consider some larger capacity steel tanks, and nitrox training. Add a pony bottle, 13 to 30 and you will be good to go.


Jim
Louisiana

I posted this as part of another longer thread. But, I didn't want it to get lost in that discussion so I'm reposting here.

The basic question is: Why not just go to doubles instead of using a Pony/Spare Air?

At first glance it seems THE way to go. With doubles everything is out of the way on the diver's back. There is total redundancy. It leaves room for another gas bottle if the specific dive profile requires it. It gives a 100% redundant gas quantity backup. It solves the travel problem because the diver is only traveling with some regs, strapping and plumbing. The extra tank is furnished by the dive operator at the destination.

I have seen this done a couple times. The diver shows up with his regs and plumbing. The dive operator provides two AL80s. The diver takes about 15 minutes or so to set up the first time, less on subsequent tank changes. Seemed to work just fine. I should also explain that none of the dive trips I've seen this on have been "Tech Dive" trips or charter boats.

I'm getting ready to spend some money. But before I do I'd like to hear what folks more experienced in this have to say.

 

[eandiver]

You're referring to shops letting out valveless tanks or unscrewing theirs? I've never come across a shop that'd do that; ones that do must be pretty rare birds. I'm curious as to packing things such as the manifold. I'd hate to allow BagSmasher Airlines have at 'em. Maybe use Pelican or hardside camera or gun cases?

That was the impression I got.......don't know too many who would. Since I have no experience what so ever with doubles I am unfamiliar with the components. Some of the dive shops here let rental tanks go out so crusty in salt they sparkle.

Pack them in the center of your bag wrapped in clothes or whatever. Only the big airports have the belt systems with "pushers". Big arms that slam a bag onto another conveyor system for routing.

 

[ArcticDiver]

Interesting replies. Especially interesting was the idea that Doubles=Tech. Never thought of it that way. Also interesting was the comment that to do doubles the dive operator would have to allow use of valveless tanks.

Re Valveless tanks: Off the top of my head I can remember at least four instances, in four different parts of the world where doubles were used as I mention. In three cases the tanks used were AL80s with yoke valves and the fourth used AL100s with yoke valves. None used DIN fittings. The diver had adaptors as part of his kit. I don't know what the adaptors looked like. But I know the valves were standard "recreational" yoke fittings because I did examine that. In fact we were all randomly swapping tanks around when they were refilled between dives. This guy traveled all over the world with his regs and plumbing he said.

Re More training for doubles than for a pony: I'll have to think about that. If the diver is going to use both tanks as part of the dive profile I think you may be correct. But in this case we are going to use the second tanks strictly as an emergency backup. In that case, from a supply point of view it wouldn't matter where the extra tank was as long as the tank was within reach . But if on the back it would be out of the way, yet easily reached. In this application that is the primary value of using doubles. If there is a question about accidentally using the Backup Tank then just leave the manifold isolation valve closed. With the tanks isolated from a gas point of view a diver is in no different situation than if there were two totally separate tanks.

 

[eandiver]

I think more training would be required to use doubles in any aspect. In a situation you would need to be familiar with which of the 3 knobs to twist without being able to see them as opposed to a visible (if slung) single valve on a pony.

If you use one of the doubles as a main source while the other is for emergencys at the end of the dive you should have one full and one almost empty would there be a off center weight problem? As I said before I haven't used doubles before so I don't know.

 

[ianr33]

I have done quite a few dives using independant doubles. I use the "Aqua Explorers Ultimate Doubles Bands" these mount very easily and securely to a backplate. My normal technique is to breathe one tank down to 1500psi and then switch regs. Surprisingly I have never noticed any tipping effect when the one tank is down to 1500. I suspect you could breathe it down to 500 and still not notice any instability if you wanted to keep one tank purely as a backup.

It is a great system for using doubles with rental tanks.I find it a more convenient system than slinging a spare 80 . The hose setup is exactly the same as manifolded doubles except there is an SPG added to the righthand tank. I put this under my right arm and clip it to my right chest D ring.

It is also good for solo diving as it is 100% redundant. I would not be too happy diving solo to any significant depth using manifolded doubles as your life could depend on shutting the correct valves FAST.

The main disadvantage is the disparaging comments from DIR types and Tech Instructors if that sort of thing bothers you. The normal phrase seems to be "Suicide Twins" !!

 

[ArcticDiver]

Now I'm really upset at us not being able to get together when I was in Texas! Seeing your rig and diving with you would have answered all my questions.