Quote: (Originally Posted by
daviddem)
Hi,
I am contemplating getting equipped with larger back gas for deeper dives.
1) What cylinders are the preferred ones among the DIR crowd in the twin 18-20 liters size? It seems people more often go for twin 18. What is the reason why the extra capacity of the 20's is not so appealing? Trim issues? What brand cylinders would you recommend?
2) Which wing are you using with such a setup? I don't believe my Evolve 40lbs would provide adequate lift with this back gas + multiple stages.
In ocean dives, for me it all comes down to minimum gas. If you can carry enough gas in twin 80s for minimum gas then there is very little point in buying new cylinders for your current dives. Eventually you will reach a point where minimum gas becomes a limiting factor for your dives - you could add an extra deco gas to reduce minimum gas or consider bigger tanks.
With a normal SAC you can do reasonable times at 80 m with a single stage, 50 and 100 and twin 80s (12s). Anything longer or deeper than this and you are probably looking at bigger back tanks. I have used 15s, 104s and 18s. I like the 15s least can live with 104s and love the 18s - that is until I start climbing out of the water - however on a dive where you really need them you probably should have someone else to lift them out the water for you
They are quite heavy full of nitrox but then on a dive where you need them they'll be full of trimix anyway
thus I have been quite comfortable in a 40lb wing and 4 stages even got lost at sea (for a few hours like this)
Of course you'll need a buddy with the same tanks
HTH
Graham