[Mark Davies]

Originally Posted by Kirstie

Paul suggested to me that I start using a single 15 instead of a 12. I've resisted so far as, to me, it feels almost like cheating, or taking a step backwards. I've got this idea in my head that I should be working to improve my consumption on a single 12, rather than resorting to a bigger cylinder.

You've got a number of options, but look at it objectively and manifolded twin 12s rarely come out as the most sensible. Too many people use poor SAC as a reason to get twins and then in reality end up doing two dives in a day on a single fill, which is in fact less available air than two single 12s!

Matt's solution of independant twins and then using a third, full cylinder for a second dive has merits, but then you're using three tanks with the transport problems involved with that (if that's relevant to you).

Some people use a 12 and a pony and then regularly rely on their pony. If you're going to do that you might as well just have a 15 and save the bother. Add an H valve and regain the redundancy you get with the pony.

Twin 7s are a cracking idea - especially 300 bar if you can get the fills. Plenty of gas, redundancy, comfort, the lot. The only set-back is you need two sets for a two-dive day and that becomes expensive when you factor in the costs of maintaining 4 tanks. And they cost a fair bit to buy in the first place.

It's all about what you need and what suits you. There's no 'cheating' about it. As Matt says, for some people no amout of dive time seems to bring down their SAC. There's no point in trying to fool yourself that you can get away with less when you need more - and there's no shame in that.