Doubles vs. Pony/Spare Air

[DA Aquamaster]

I have also traveled and used a set of travel bands (Aqua explorers) with single rental tanks and that approach offers a lot of flexibility.

You can do a deep/long dive with independent doubles and manage the air by breathing one tank down a third, switch to the other and use two thirds of it, before switching back to use the remaining 3rd in the first tank (which leaves a 1/3 reserve in each tank).

Alternatively, on a single tank recreational profile, you can do the whole dive off one tank and use the other as essentially a really big pony. On the second dive, (if a fresh tank is not available) you can use the second tank and use the 500 or so psi left in the first tank as the "pony". If a fresh tank is available, you can quickly change out the one you used and do the second dive with two full tanks.

In either case, you have redundancy, can function effectively with generic rental single 80's and avoid the need to travel with a pony or tools or to install manifolds at the destination.

I have not had any trim significant trim issues with either AL 80's or steel 72's when breathing one tank down to 500 psi and leaving the other full. There is a 4-5 lb swing in bouyancy, but it is still close to center line and does not impart any great tendency to roll to either side.

 

[budgy]

For a 2nd long dive I've a buddy jacket that accepts two independant 12's. Though It's a bit heavy for some shore diving particularly if the access is difficult. Shallow diving, with a single I leave the bcd and pony behind these days, I'm using a back-pack and a suit inflator for buoyancy. I'm considering getting the pony O2 cleaned and getting it filled with 100% for emergencies.

 

[matt_unique]

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.

There are only 2 reasons I can think of why you would go with a pony over doubles: weight and gear limitations. I use a single and a pony when doing shore dives because I don't want to bust my a** trying to walk my doubles set over slimy rocks. I also use a single and pony when on vacation. You may also go with a pony as a best alternative if you do not have the gear for doubles (obviously) including your backplate and wings.

Independant doubles would be great for vacation boat dives.

--Matt

 

[ArcticDiver]

Thanks everyone.

You've confirmed my initial assumption. Not sure just what hardware I'm going to buy. But my backup gas is going on my back, out of the way.


Side comment:
It seems the only real reasons to sling a tank are:
-Use as a Bailout Bottle for Public Safety Diving or the like.
-Need the Gas for the specific dive profile (Deep, long, different gas mixes, etc)
-Personal Preference.

 

[DEEPLOU]

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" !!

I use the "Aqua Explorers Ultimate Doubles Bands"

Around here we merely refer to them as "Berg Bands"
When I first started to use doubles that's what I used, but I then invested in manifold and steel bands. The Berg Bands are still close at hand in case I need to use my AL 80s in addition to my two sets of doubles, and when I fly away and know I will be doing some dives that will require the safety of doubles.

When using tanks w/3000psi I like to do it in thirds. First tank take from 3000 to 2000psi, then switch and the second tank go from 3000 to 1000psi. If at that point still in water, switch back to tank one. This way you should have ample reserve if either should malfunction.

 

[100days-a-year]

I don't use doubles for several reasons.Cost alone is one.I do approx 250 dives a year and 150 or so are with a slung pony.At 2 fills per dive for doubles @ $3US per fill for nitrox I save about $300 a year as I use big singles and the pony is just that..redundant.Therefore rarely gets used.An HP 120 or jacked up LP98 gives me more than enough gas to do NDLs to 150' or even short(less than 15min)deco.
Another reason is that on small boats (less than 30')doubles are a serious PITA esp in any seas over 2'.Too much mass and bulky to boot.A stage can be placed conveniently along a gunwale where you can sit and sling it.Doubles must either be worn or carried from where stored.We tried for several years and only one buddy was ever comfortable moving them around but he was 6'4 and 280 and really needed the xtra gas anyway.We ended up jacking up a Lp and a HP set for him and transfilling the LP set after dive 1 to get away with only carrying 2 sets of doubles.
As for travel we trailer my boat and take all our gear, no need for airplanes when you live in Fla

 

[hex92]

Thats my biggest concern about doubles....The weight and bulk of them. Getting around on a crowded dive boat and then having to haul your *** out of the water in heavy seas is much more difficult with doubles vs a pony. Thats why I am sticking with the pony for at least a while longer.

 

[100days-a-year]

We would usually tie off the doubles and then 2 of us lift them in over the side.I have walked up ladders with doubles on but it's a serious load.You can unsling the pony at the anchor line or ladder pretty easily and lose 20# if you have to.

 

[matt_unique]

Thats my biggest concern about doubles....The weight and bulk of them. Getting around on a crowded dive boat and then having to haul your *** out of the water in heavy seas is much more difficult with doubles vs a pony. Thats why I am sticking with the pony for at least a while longer.

Especially in rough seas it is much easier to exit your rig on the surface, tie it to a trail line, then hoist it up from the swim platform.

--Matt