Captain Calamity(Offline)

Thanks for the replies so far, and for the warm welcome.

I dive out of Portland, and haven't ever had more than one dive per boat ride, so the two dives per fill issue is something I hadn't really considered, but equally doesn't really apply to me. I didn't mention earlier that I do an awful lot of shorediving with a friend who doesn't dive much deeper then 15m - and there's no way I am taking a 12L twinset for that. In reality, I doubt that I will be doing more than three or four dives/year in the UK > 30m.

Given that I already own my own wing, regs, and would buy my own wing that suited both 7s and 12s, would there really be a huge difference between swapping twin 7s for twin 12s? I would make sure I buy the same manifold that the hire shop use for my own personal 7s, so the only actual difference would be the weight and size of the cylinders.

After looking at the responses to my first post it seems to boil down to which set of equipment would be right for me the majority of the time - given my established pattern of diving I still tend towards the 7s, as almost every time 12s would be overkill (I cannot image lugging them into Chesil Cove for example!).

If (and here I have to trust you all) the difference between twin 7s and 12s is enough to be dangerous when using the 12s just occasionally, then perhaps there is some merit in using the 7s for everything and taking a stage bottle on the odd deeper dive that I do, even if it is more hassle for a similar amount of gas?

I am not sure that I can justify the expense of keeping twin 12s that I use just three or four times a year, on top of a single tank setup, whereas always diving the 7s would keep my valve drills sharp and should mean that I always have a redundant air supply.

CC