Quote: (Originally Posted by
Gilles)
One should carry adequate bailout gas, but ...on the same token, one shouldn't be taking excessive amounts either. 100% redundancy is over the top IMO.
If you and your buddy(ies) are on CCR, the liklihood of both units going off at the same time is about the same as that of complications caused by carrying too much gear with you
.
I like to use the following bail out design parameters.
Plan from furthest distance and latest time from safe exit route on bottom (e.g. 10 minutes away from up line 10min before start of planned ascent)
Bottom RMV of 40 L/min (includes about ~3x excess)
Deco RMV of 20 L/min (includes ~1.8x excess)
0 conservatism on the B/O deco profile (on the premise I can pad the shallower stops depending on actual gas consumption)
Use team approach. Don't do dives that need a good team, without a good team
. Bare minimum of 1.5x gas requirement for one member of team
(or solo).
Dive Safe
Ditto
I own:
2x3L - both with air
3xali40's - O2; 50; and 18/35
6xali80's - 02; 50; 30/35; 15/55; 11/60; 7/70
To start - you have to do the planning to get yourself out of thw water alive in the worst case senario. Certain environments make this easy others not.
Depending on the environment and the depth, will determine what I use. (These dives are all done on the principle of solo diving). On shallow (<40m) I'll use one or two 3L (two for moderate deco), for any moderate length dives in the 30 to 60m (ocean or cave I'll use all three ali 40's (really light and not in the way and with a 50 and O2 available I can get out of the water really quick). But on a long penetration dive I may end up staging some 6l and maybe even the equivelent ali 80's.
On a 100m cave dive I'll end up staging/carying all the ali80 and sometimes even the ali 40's (and I'll carry one of the 3L's as dry-suite and backup wing inflator. It really depends on what you need to survive.
Note however that too many cylinders could be a danger if it is going to increase your task loading. It is very difficult to battle a current at a 100m whilst slinging 4 x ali 80's.
If you do not have the gas do not do the dive. You have to be able to get yourself out of the furthest point of the cave/hole and have some gas left.
On deep diving (if diving in a team) we will carry our own source of bailouts for the deep portions, i.e all gas required up to say 60m as these gasses are depleated very quicly at depth and a minute looking for gas (which your buddy is carrying) could be a minute to long and thereafter we will use team gas planning (i.e enough gas to get one or 1.5 divers out of the water on OC or make use of an emergency back up diver drop bottles for the O2).
To answer your question: If I had to buy just two cylinders I'll buy 2 x ali 80's as the trim is spot on and they give as much gas as could eb reasonably expevted from a bailout cylinder. However if you are reasonbly sure you are not going to go really deep and long 2 x 6 or 7L may suffice - but these cylinders will limit you if you want to go deeper. But do not sell your 7's as you'll always find a need for them.
Cheers Dries