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<brm@yo*.co*> writes:
> Everyone seems to have missed the point on this one. Will's implementation
> of the last stop depth is not quite what you would expect. Unlike other
> programs, ZPlan seems to rearrange all of the other stops instead of just
> the last one. If you set the Voyager last stop depth to 15 feet, you would
> get stops like this: 40 feet, 30, 20, and finally 15. Do the same thing
> with ZPlan and you get stops like these: 45, 35, 25, 15 feet. So not only
> is your last stop deeper, but all of your stops (45 minutes worth, including
> deep stops) are 10 feet deeper with a last stop depth of 6m instead of 3m.
> That could easily add 15 minutes onto your total time. The Buhlmann model
> is optimized by going as shallow as possible as quickly as possible.
No, that setting simply sets up the list of depths at which stops could
be done; if (as I just did to verify) you do two runs, changing
LastStopDepth between them from 10 to 20, all your other stops stay the
same. A 40 foot stop is still a 40 foot stop, with exactly the same deco
obligation to clear, and ZPlan moves you up to 30 feet as soon as you've
cleared it. The only difference, given that your whole dive is on air,
will be that the one schedule has 20 and 10 foot stops, and the other has
a (much longer!) 20 foot stop from which you go directly to the surface.
The key point, though, is that there's absolutely no way you'd want to do
any sort of significant deco on air. Go to oxygen at 20 feet and,
besides saving huge amounts of deco, a 20-only schedule now becomes
quicker by a slight margin.
(Disclaimer: if you've never decoed on oxygen, get a competent instructor
to teach you the ropes; there are significant dangers that you need to
know how to avoid.)
(For a quick test, throwing in 100 feet for 100 minutes on air, no
intermediate deco gas, and whatever ZPlan settings I was using last time
I played with it, I get the following total deco times:
74 minutes, with oxygen at 20.
76 minutes, with oxygen at 20 and 10.
170 minutes, with air at 20 and 10.
280 minutes, with air at 10.
and as you can imagine, NOBODY does the 280 minute version and virtually
no techdiver would be caught on the 170 minute version either. Further
savings could be made by using nitrox appropriately.)
--
Anthony DeBoer <adb@on*.ca*>
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