Single vs doubles.

[Rhone Man]

I'll skip through the patronising comments about what is wise and what isn't (not disagreeing with what others have said, but I say we all make our own choices on risks...).

I bought a set of doubles for the "more gas" theory, and ended up backtracking and just getting a larger single tank. Doubles are a lot more expensive and a lot more hassle, and a lot more gas. If you just need a "little more" gas, just buy a bigger single tank. If you just need some emergency redundancy for solo, use a pony. If you are doing planned deco, OK, now you are entering the realm where doubles become more advisable despite the cost and hassle. (Although if you have a good SAC rate and can string out your backgas till you get to 15 feet, you can get nearly 30 minutes of deco out of a 19 cu ft pony in optimal conditions. YMMV.)

In terms of cost, with doubles, everything is more expensive. Not only the tanks, valves and bands (obviously), but every fill and every VIP usually gets you charged a premium too. You will also likely to need to buy a new wing and (if you aren't using one already) a backplate. If you only need an extra 25 cu ft of gas, query whether it is worth it. And they are a significantly greater pain in the ass to lug around unless you are fortunate to employ a Tibetean sherpa.

 

[Scubadude_LA]

Linedog, Welcome to the solo thread

Swapping tanks could be solved by doubles provided you don't breath them down far enough not to be able to make the next dive, basic gas management, also hard to manage physically in some situations. They are a double edged sword that can hurt you if you assume you know how to use them but don't. I'm not sure how they would help the "SI" portion of your issue though, nitrogen is nitrogen, like a hangover, only time cures it.
Good posts above We need to know if you are OW or have some tech/deco training?? If not stick to NDL with enough redundant gas to surface anytime. Solo is way good IMO properly executed.
Cheers