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At 09:04 PM 10/09/1998 -0000, Jim Cobb wrote: >Billy- > >There are situations where you do no-stop penetration diving (people do >it around here all the time on shallow wrecks) and in those situations I >will maintain that doubles are the way to go. I agree. Any overhead environment, whether physical or decompression requires doubles. The big single cylinder and pony combination for those kind of dives shows appalling dive planning skills. The question is what kind of doubles? That guy was asking about manifolding together two little 7 LITRE bottles. These are no bigger than swollen pony bottles. Why anyone would go through the convolution of manifolding two tiny tanks together escapes me. Maybe they saw it on tv and thought it looked good, or something. I agree that double 72's >are unsuitable for deep deco dives but IMHO are fine for "shallow" deco >dives. Nooooooo. You musn't mention 72s. Not the 72s. This is a metric thread. LITRES and BARS only. rgds billyw > > Jim > >On 9/8/98 7:36 AM bdi wrote: > >>At 03:09 PM 7/09/1998 +0300, Teppo J Kurki wrote: >>>Having gone from 10 l/300 bar tank to 2x7/200 and now own also >>>2x10/200 here's my thoughts: >>>15 l >>>+ cheaper (probably) >>>+ a little more gas >>>- valves hard to reach (at the back of your neck) >>>- awkward because of large diameter (at least in my experience) >>>- need more weight >>>2x7 l >>>+ fit closer to your body => better balance >>>+ reaching valves a lot easier, since they stick out >>>+++ when you get larger doubles you can use _exactly_ the same setup and >>>you will have already mastered the right reflexes >>>- heavier on the surface >>>- more expensive >> >> >>TJK, the problem I have with the two configurations >>mentioned, the 15 litre single and the 7 litre doubles >>is in the ocean the 15 litre is too big. Unless the >>user is an unfit, incompetent hoover with enormous >>air consumption who shouldn't be diving, they won't need >>all that gas on any reasonable singles dive- no overhead, >>no deco ceiling, within bail-out reach of the surface. >>A 10 litre is plenty big enough and doesn't give you the >>management problems with the huge tank. >> >>I use a 65cu ft alloy on those kinds of dives and >>that holds enough gas for me to earn a deco obligation. >> >>Also a 15 litre single is useless for caves. >> >>The two 7 litres are too small to do any reasonable >>decompression or overhead dive, (rule-of-thirds gives you >>only a bit over 900 litres of gas to turn-around). >>At a useful planning consumption of 15lpm that's 12 minutes >>at 40 metres. For all the convolution of doubles, and >>two sets of regs, you might as well twin a couple of >>10s or 12s and either get a reasonable dive in or leave >>yourself a better margin. >> >>In the one post, this guy came up with the two worst >>cylinder configurations imaginable. >> >> >>rgrds billyw >> >>-- >>Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. >>Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. >> > > > ------------------------------------------------------------------- > Learn About Trimix At http://www.cisatlantic.com/trimix/trimix.html > > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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