Basically a pair of plastic spacers that go between the cylinders with standard cam bands to hold them. You either strap the set to whatever backplate/BCD you are using or you can buy adapters if you want to bolt them on. I can't recall who makes the adapters, might be Custom Divers.
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I use a very similar style of bands for independent doubles. I used a single tank adapter instead of those plastic pieces, but the configuration is largely the same.
I found it reasonably – but not completely – stable. There is definitely a lot more wiggle than there is with a pair of steel banded doubles. But that wasn’t really an issue.
The issue came down to two things: one, the valve handles are backwards on one of the tanks, which makes the idea of shutting down that tank very difficult, if not impossible. If you’re not worried about the redundancy that comes from being able to shut down a bottle, that might not be that big of a deal. I suggest breathing from that regulator/tank first.
The other issue was the need to balance between the tanks. Doing it every 500 psi is overkill: it doesn’t throw off your trim as much as it would with sidemoumt. But you do need to balance the usage, not least for safety. That may have something to do with why they want you to have so many extra regulators: if you breathe the tank down to zero, they want to know that there’s still a secondary regulator on the other tank. In other words, they don’t trust you to use them correctly. Honestly, why should they?
And that, to me, is the real Achilles’ heel of this configuration. It’s a lot of screwing around. You keep telling us how you’re worried that you’re gonna lose your situational awareness because of the “beauty of the reefs“. That means we can’t count on you – by your own words –to do your job properly. And that can very much end in a rough situation. Either you breathe down a tank without realizing it, or maybe you do realize it, but now you have an empty tank on your back and if someone needs air, it’s going to be a struggle to make sure that you are able to give them a workable regulator.
You haven’t trained for this and you haven’t practiced this — and no, a single pool session where you have no risk of distraction and without the buddy you’ll have with you on your trip does not even remotely count.
Independent doubles can be made to work. If I literally could not in any way get anything other than aluminum 80 scuba tanks, there’s a high degree of likelihood I would break out my independent doubles tank bands and use them. It’s literally exactly why I built them: to be able to dive doubles when I couldn’t get manifold back mount doubles when I travel.
But I can tell you that I would put a *great* deal of effort into finding a better alternative. They have some small advantages, but they come with some significantly sharp edges. And honestly, I haven’t had to use them in probably close to a decade: it just isn’t that hard to get manifold back doubles anymore anymore. And I’m grateful for that: because they work so much better than rigged together individual scuba tanks strapped to your back.
ETA: I just realized: I built these before I became proficient at using a stage bottle. And I have not used them since I became proficient at using a stage bottle. I can tell you right now, I would much rather sling an AL 80 as a stage, rather than use independent doubles.
@tursiops for the win!
I get it: all you’ve got are square pegs, and you want a way to make your square pegs work. And all everyone here keeps telling you is that really you need round pegs. I really do get it. You’re signed up for a dive of a lifetime, halfway around the world, the money‘s been spent, and you just wanna make the most of it. You don’t want to hear that you should be able to make an AL 80 by itself work like everyone else. You don’t wanna hear that you really, really should be leaving that camera behind because you’re just not ready for it. You want what you want, and you just want a way to make all of those pieces come together.
And it’s entirely possible that independent doubles may allow you to meet those needs. But it won’t do it without exacting its own cost. It will be more cumbersome, it will be more risky, and those risks literally could lead to a very serious error. I’m not saying you shouldn’t do it. I am saying you should read the objections that are being given to you very carefully. Understand them. Do what you can to mitigate them, by adjusting the equipment and improving your training between now and then. You have plans that may allow you to do that. But don’t get buck fever: don’t focus on this solely as the solution to your problems, while ignoring the problems that it will bring about along with it.
