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At 05:21 PM 6/12/00 -0400, Capt JT wrote: Hello JT, >I used mixes as follows >10/60 bottom mix >20/20/60 as travel to 100ft and then as my deco gas on return >starting at 230ft >32% at 130ft >50% at 70ft >100% at 20ft >I ran a 12 minute BT and that starts when I reach the wreck, my run time >was 115 minutes and I got out of the water. Decoplanner, with default 30/85 GF, gives the following: Bottom Run Time Time ================= 12 111 13 121 14 132 Notice that each minute on the bottom adds about 10 minutes to deco. At depths beyond about 300 feet you run into these very steep curves which require more precision in everything from your mix (a 2% variation in your FO2 at 400 feet changes a PO2 of 1.3 to nearly 1.6) to your bottom time. Counting bottom time starting when you hit the bottom doesn't work well for dives in the >300 foot range because every *six* seconds of bottom time equate to ~one minute of deco. The time you spend on the way down on dives of this magnitude significantly add to the gas-loading. The 60 seconds you spend on the way down from 300 feet to the bottom at 380 alone add about seven minutes to your deco. On shallower dives, counting bottom time starting on the bottom works because the curves are less steep. In the time it takes to get from the surface to 200 feet, for example, gas loading is not significant. This is why you can get away with beginning your ascent *about* on time, and staying an extra minute or so is no big deal. At 400 feet, staying an extra five seconds ads about a *full minute* to your deco. This is especially true on bounce dives where the compartments pass only the first few half-times (and don't approach saturation) and are on-gassing most quickly. I usually count bottom time starting when I get to the bottom *except* when the dive is deeper than 300 feet; when I dive below 300 feet, I count it from the time I reach ~200 feet (when the curves begin to steepen). -Mike Rodriguez <mikey@mi*.ne*> http://www.mikey.net/aue Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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