How do you rig and use your doubles?

[Sawdust82]

I dont have any experience with double tank setups, but am interested in getting into it in the future (read: after many more dives, and much more experience and instruction). I have a friend that is an instructor, but she lives in germany and only visits in the summer months, so sitting down to chat about it with her isnt really an option at the moment...

Ive ran into a few sets of manifolds and bands for sale used in my quest for a set of standard rec gear, and am wondering if any of it would be useful to pick up for later use...

My rough plan at the moment is to round up a small fleet of used al80s to have enough tanks for a full weekend of diving without having to go looking for fills. They seem to be fairly plentiful and cheap in my area (im on a budget), and i dont see many steel tanks around here for sale used. My LDS is a three hour round trip, and if theyre busy i would have to leave them and come back to pick them up. If i have to do that id like to end up with a good supply of air for lots of dives once im done driving around. I havent bought any tanks yet, but am considering a few.

So then with some used doubles stuff floating around, it got me wondering if i could/should eventually double up a couple al80s to give longer bottom times. Would likely be at fairly shallow depths, scallop diving and the like. What should a guy consider for this? Is it even a good idea? What ways can you rig a set of doubles on your back, and why would you do it?

 

[KevinNM]

Doubles normally mount to the backplate on a BP&W. There are other ways to do this from what I understand, but I've never see those in use.

 

[Sawdust82]

I have yet to get a bcd, and im leaning towards a bp/w anyway... Im 6'5" and 250lbs, so most of the used stuff doesnt come close to fitting me. That and boots and a hood im likely going to buy new.

Does the weighting and wing capacity have to change with a doubles set?

 

[RyanT]

Yes, your weighting and wing capacity can change dramatically depending on the set of doubles you use. A set of AL 80s makes for a nice set of doubles. They are cheap and will not overweight you like a set of steels will. AL 80's are floaty though. Depending on how much rubber/dry suit you wear, you may however, find yourself too light at the end of the dive (e.g. will need to wear some additional lead). Steels will typically make you quite heavy. I have a set of Asahi steel 100s. Even when empty, you could anchor a battle ship with those things. For most of my dives I've moved to a set of steel HP 80s. I can dive these with a 7mm wetsuit and be just about perfectly weighted. In a lighter wetsuit, they make me a bit heavy but still easily manageable.

In learning to dive with doubles, there are really two issues. One is just figuring out your weighting and trim, which can be very different from what you're used to on a single tank. Second is learning to handle a second regulator (bungied around your neck) and manipulating your valves. Neither of these are overly difficult. Ideally you just need an instructor or capable mentor to get in a pool or shallow water and help you work it out.

 

[Sawdust82]

Ill be wearing a two piece 7mm suit, likely with boots, gloves, and a hood.

I assume when you mention manipulating valves, youre talking about isolation manifolds. Ive seen ones like that, with posts for two first stages (what are they called?), and ones that seem to simply couple two tanks together with a spot for one first stage... One that im looking at simply has two yokes to couple two single tanks, tightened with a wrench, and a spot to hook a first stage. As opposed to being a pair of valves that thread into the tanks like usual, replacing the tank valves.

I guess thats what im really wondering, what are the different ways people rig doubles and why? Is it mostly to gain bottom time, or more/also about gear redundancy? Is there a standard "the way everyone does it", or do practices vary somewhat?

 

[RyanT]

I assume when you mention manipulating valves, youre talking about isolation manifolds.

Yes, exactly.

I'm not sure I'm 100% following your general explanation, but I think we're on the same page...here's the breakdown. Back in the day, you could get manifolds that screwed into the two tanks and offered a single outlet to attach just one regulator. This effectively turns two tanks into one. The only thing you gain from this configuration is more gas.

Modern manifolds connect two independent valves together with a manifold isolator knob in between. Each tank has it's own regulator attached. When the isolator valve is open, you can breathe both tanks off one regulator (the two tanks are effectively one). If you have a problem (regulator free flow, o-ring leak, etc.) on one tank, you can quickly close your isolator knob and now your two tanks function independently. This saves your remaining gas in the unaffected tank. If the leak is relatively slow, you can then reach back and turn off the valve on that tank. With that done, you can now open your isolator valve and resume breathing all the remaining gas in both tanks. The valve on the tank turns off the gas to the regulator only, but still allows it to flow across the manifold to the other tank. This system has the effect of doubling your gas and simultaneously providing a built in redundancy.

Some people do still dive independent doubles. In this case, the tanks are doubled up with bands, but each tank valve is completely separate from the other. You'll still use two regulators, but now you must switch regulators to access gas in your two tanks. You'll actually do this fairly often to keep your tank pressures relatively balanced, this avoids one tank from getting too light and throwing off your trim. This is also how side mount works, the tanks are just clipped off on the sides instead to banded together on your back. The disadvantage of this system is that if you lose a regulator to malfunction, you cannot access the gas in that tank through the other regulator.

 

[RyanT]

If you are diving relatively shallow (especially 60' or less), I think you'll find yourself a little light at the end of the dive with that much rubber and double AL 80s.

 

[tbone1004]

Read up
Equipment Configuration | Global Underwater Explorers

if you're 6'5" you basically have to buy a Deep Sea Supply backplate to get the long pattern. I'm a bit shorter at 6'4" and diving normal length backplates is extremely uncomfortable.

Weighting and wings will change because it isn't the wing capacity, is the wing shape. Doubles wings are much wider to accommodate and if you're doing it on a budget you should commit to one or the other imho.

I don't believe in 7mm farmer johns and don't think they're safe, but that is neither here nor that. Part of that reason is that you need a very large wing to safely dive said wetsuit at depth and it severely limits tank selection to protect yourself from getting dangerously overweighted. In doubles you rarely have any extra lead to "ditch" so if your wing fails, you have to swim the rig up and most people can't do that. With the 7mm farmer john you are basically limited to AL80's or LP72's at this point.

now. I dive doubles, I dive doubles a lot, just not in caves. I have a set of independent doubles mainly for convenience of being able to remove them for sidemount. I also have "normal" doubles. I am a firm believer in the GUE/DIR/WKPP whatever alphabet soup you want to follow today for their backmount configuration. They figured that out over many decades of extreme diving and it works for 99% of situations where backmount is appropriate. I used to not believe that, but then I found out about the long pattern backplates and my world changed because I had gear that fit me finally and could get out of it easily and efficiently. There are some things I disagree with in there, but the general gear configuration is damn good.

With the sudden popularity of sidemount over the last few years, bands and manifolds can be had very cheap compared to 5 years ago when people were still regularly diving doubles which is good for those that still want to dive it. That said, if you are trying to extend bottom time, sidemount may be worth looking into. Look at your long term diving goals and by gear based on that. You will not out grow any of this equipment *except for exposure protection, but then you should get on a treadmill ;-)*, and it will last a lifetime.

 

[Sawdust82]

Thanks for the link and the help guys, i learned a lot tonight.

These are the specific manifolds i was referring to. Im guessing both sets are fairly old?

 

[Dave Bevan]

I would recommend seeing if any GUE instructors in your area offer the Doubles Primer. I did this and it showed me a lot about configuration and particularly getting the weight right. Also it will show you which equipment is right which will save you money in the long run or prevent you from diving with dangerous gear configuration because A) you already bought the gear and will be damned if you aren't going to use it or B) Just don't realise that you are dangerously over weighted.

Once you know what you need you can build it up over time. The course is relatively inexpensive and only takes two days.