I’ve dived independent doubles, manifolded doubles, inverted doubles, isolation manifold doubles in wetsuits and drysuit with and without buoyancy compensation. The most extreme setup is in the photo, O’Dare 7mm hooded jacket over a 7mm longjohn 14mm of hard neoprene with heavy steel twin set, no weights and no wing. I dived it to 54m and you need to be able to swim the weight off the bottom at the start of the dive but it’s not as extreme as people think. If you need to hold a deco stop at10 feet you can’t breathe the tanks down past 70 bar, if you do the last stop will have to be on a rope or 20 feet. I wouldn’t dream of diving like this again. The nicest setup for you wet in the depth you’re planning would be a small wing with a manifolded pair of 7s. But have a try with what you’ve got to give yourself an idea of what it’s like to carry twins and make reg switches.
Tips on starting diving doubles
- Thread starter SouthernSharktoothDiver
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halocline
Contributor
Those bands look a little familiar, lol. I know I sold mine a while back.
Anyhow, a word about bands for LP72s; modern 7” bands work fine. In fact, I used the same set on AL80s (7.25”) without any problem at all. I had to get slightly longer bolts. I honestly don’t know if it would work the other way, using 7.25” bands on LP72s. The plates would be pretty close together. You’d need short bolts for sure. In terms of spacing for the manifold, modern manifolds have an adjustment range and I had no problem using the same manifold on both the LP72s and AL80s.
AL80s make pretty decent doubles. I far prefer LP72s over AL80s as single tanks, so I assumed that LP72s would be better as doubles too. But I was wrong about that, the AL80s are better for trim and balance for me. A set does weigh 6-8 lbs more on land than the 72s, no getting around that one, and you probably have to add about 4-5 lbs in weight, so overall 10-14 lbs more to lug around. It’s nothing like big steel doubles, though.
Do y'all even read the OP? He outlined the conditions he'll be diving in.... 30 ft, hard bottom, slope to shore, within NDL. A number of you are berating any idea or methodology that doesn't support your expectation that this is for tech diving.
This isn't just in response to the quoted text (or the quoted individual).
Kinda like the hyperbole... One individual when bashing the idea of cheater bar manifolds actually admitted they never used one (just thought it looked stupid... Plus gratuitous swear words).
halocline
Contributor
If we’re strictly talking about the OP’s current dive scenario, obviously single tanks make the most sense. Maybe with a small bailout bottle if you’re paranoid that you couldn’t swim up 30 ft. I used to do these sorts of river dives in TX and I liked a single LP72 or AL63 just fine for that type of dive.
But I believe the OP wants to learn about using doubles, maybe expand his diving in the future, etc. So it’s certainly fair game to criticize ideas that don’t make sense. And yours definitely does not. For doublehose vintage diving, a center outlet manifold on small doubles was a common set up and really fun to dive. But that’s a totally different situation than we have here.
Eric Sedletzky
Contributor
I just put this set together.
Ignore the plate, that's just my own non DIR compliant garbage. You could put a regular plate on that set as well. Actually, everything about me is non DIR compliant garbage.
Look at the 72's and the solid bar manifold. This is essentially just one big tank split into two halves with one center post. If you want redundancy then go to your buddy or sling a little bottle on your side. I'll get 144 CF but the advantage is it will balance out well and not be one huge water heater style single on my back which could have a tendency to turtle, like an 8" Faber 149 that's the biggest they make.
When the weather finally lets us get in I use this in a 7mm wetsuit for shallow urchin diving (up to 30-40').
Wet steel, Oh god, the children!
Ignore the plate, that's just my own non DIR compliant garbage. You could put a regular plate on that set as well. Actually, everything about me is non DIR compliant garbage.
Look at the 72's and the solid bar manifold. This is essentially just one big tank split into two halves with one center post. If you want redundancy then go to your buddy or sling a little bottle on your side. I'll get 144 CF but the advantage is it will balance out well and not be one huge water heater style single on my back which could have a tendency to turtle, like an 8" Faber 149 that's the biggest they make.
When the weather finally lets us get in I use this in a 7mm wetsuit for shallow urchin diving (up to 30-40').
Wet steel, Oh god, the children!
Maybe for you, or me, or some others... on the other hand, 2 tanks you already own are far cheaper than a niche market giant tank you don't. Regardless of that aspect, there's also the differences in buoyancy, trim, and dry weight for different configurations of tanks for a given capacity. I'm not trying to tell him what is best, I'm just offering an option to see how the double 72s he owns feel in the water.
Again with someone's belief of what the OP "really meant" being used as justification to attack an idea that doesn't fit their own. How about we address ideas on their pros and cons... actual merit? Then the OP will do what all of us will do anyway... make his own decision.
Whether the option I offered up makes sense depends on your goals.
Cheater bar pros:
Cheap (available to try free, uses tanks and bands OP already has).
Allows individual tank swapping to get max use out of partial tanks.
Lets 4 individual tanks get used as 2 sets of doubles in sequence without having to buy another manifold or dedicate those tanks to always being doubles.
Simple operation (task loading is the same as single tank due to single reg set).
Cheater bar cons:
Less secure than dedicated manifold (though it is pretty stout, I can carry double 72s by the cheater bar with zero concern about shifting it).
Does not provide redundancy.
Places tank valve handles facing strangely (one towards your back and one straight back.
With that in mind, I would not advocate for the cheater bar approach for overhead/confined areas, or as a step towards tech. For NDL pure recreational settings not requiring personal redundant air, it can be a chance to see about the weight/trim/buoyancy of a given tank set without having to assemble a modern manifold or to increase total volume of available gas. It can also be a method in the above conditions to maximize use of fills (pairing partial fills with a new fill or another partial to get a reasonable dive out of them).
Being as I don't do tech or dive isolator manifolded doubles, I genuinely would like to see a similar breakdown for them.
Respectfully,
James
@SouthernSharktoothDiver,
Will you be carrying two SPG's when you're diving BM independent doubles? If so, how will you configure them? One on each hip? One over each shoulder? One under each armpit, attached to your harness chest straps? Some other way?
And have you selected your regulators? FWIW, a Poseidon Odin regulator 2nd stage has no "upside down" or "right-side up". And, some other 2nd stages can have the regulator hose easily switched to connect from the left side.
rx7diver
Will you be carrying two SPG's when you're diving BM independent doubles? If so, how will you configure them? One on each hip? One over each shoulder? One under each armpit, attached to your harness chest straps? Some other way?
And have you selected your regulators? FWIW, a Poseidon Odin regulator 2nd stage has no "upside down" or "right-side up". And, some other 2nd stages can have the regulator hose easily switched to connect from the left side.
rx7diver
OP
SouthernSharktoothDiver
Contributor
@rx7diver I will be carrying two SPG's, yeah. Current plan in to run them under the armpits, to each lapel D-ring (so basically my current setup mirror across). Alternatively, I have considered acquiring a small, light SPG and banding it off to one reg, which will remain on my necklace holder, but that feels too bulky. Gonna start with lapel positioning and move on if that doesn't work.
As for the regs, running on my right will be my conshelf regset, and on my left, I think my Tusa regset can have the hose connected on the left side, though I want to double check that with my LDS (who sold it to me) so I don't tear up my reg.
As for the regs, running on my right will be my conshelf regset, and on my left, I think my Tusa regset can have the hose connected on the left side, though I want to double check that with my LDS (who sold it to me) so I don't tear up my reg.
@p_kos,
That's a shame. I'd like to read your dive report if you ever do dive these indep double 72's!
You're in Ontario, so you're probably diving dry. (Is this correct?) I think of double 72's as being a wetsuit rig. At one time I dove double HP100's dry, which I enjoyed very much (though, at 24" tall, they were a bit short for moi).
rx7diver
Keep in mind your left side can get a bit "crowded" (since you will be operating your BC inflator from your left side, probably). I ran both of my 2nd stages from my right (since I was used to doing this from my tech diving). If you, too, decide to do this, then you've got to be able to make sure you're breathing off the "correct" cylinder.
rx7diver
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