On Wed, 10 Sep 2003 12:03:24 -0400, Lee B ell <[log in to unmask]> wrote:

>Huw Porter wrote"
>
>> For single square(ish) profile dives, my tables (Buhlmann with GF 20/90)
>> give more deco than my Suunto Stinger.
>
>> 27 minutes at average depth about 33m on nitrox 32.  (ran on the schedule
>> for 25 at 35 fudged slightly)
>>
>> Table deco:
>> 2 @ 24
>> 1 @ 15
>> 1 @ 12
>> 1 @ 9
>> 5 @ 6
>>
>> Stinger ceiling cleared during the 9m stop.
>
>There's something odd about what you wrote, or at least what I think you
>wrote.  If I read you correctly, you used your tables to set the profile
for
>a 25 minute dive at 35 meters, about 115 feet, on nitrox 32, which yielded
a
>deco schedule totalling 10 minutes with the first stop at 24 meters.

More or less.  With the settings I've been using, the 32% tables for 25
mins at 35m, and for 30 mins at 30m both give a deco profile which looks
something like one min at 15m, one min at 12m, one min at 9m and 5 mins at
6m.  This then extrapolates neatly to 27 mins at 33m.

The 24m stop is a microbubble stop, halfway between max depth and first
formal stop.  There is no second microbubble stop, cos it would be 24m
minus 1 ATM, or 14m which is above the first formal stop.

>First, I do deep stops beginning at about half my maximum depth.  In this
>case, I would not have done any stops until somewhere around 15 meters,
>about 50 feet.  Interestingly, this was the perfect profile to demonstrate
>why.  During my 30 foot per minute ascent, some compartments continued to
>load and just before I hit 50 feet, I got an extra minute of deco.  In
other
>words, one or more critical compartments were still loading at depths below
>50 feet.

Yep, but you either have to run with the 'deep stop' idea or not.  However
the computer/tables model loading or unloading compartments, within my
(limited) experience, and within my (admittedly 'weenie' profiles) I know I
feel good after adding in deep stops.

I'm certain this approach isn't perfect, but equally I'm certain it is
better (and involves a lot more 'computer between the ears') than going to
the computer ceiling and staying there till the computer clears.

>  Further, when I ran a 25 minutes dive to 115 feet on 32% on my
>computer, it reported only 3 minutes of deco at 10 feet, added a minute
>before I hit 50 feet and dropped back to 3 minutes before I got to the
>mandatory 10 foot stop.  When I ran this dive the way I actually would have
>done it, with 2 minutes stops every 10 feet beginning at 50 feet with a 3
>minute safety stop at 15 feet, my computer cleared deco during the 30 foot
>stop and was nearly out of the caution zone by the time I hit the surface.
>
>I suspect we're talking apples and oranges here.  I find it hard to believe
>that your tables and/or computer are that much more conservative than my
>Oceanic and Genisis computers (which both use the same algorithm).

It depends on the setting used, most specifically the gradient factors.  I
personally choose conservative gradient factors.  The same profile using
40/100 for example generates just 3 mins of stops, 1@9 and [log in to unmask]  Using
10/70 gives 17 mins including 13 minutes at 6m...

The Stinger still cleared before the table profile was complete, possibly
partially because the average ascent rate between stops was a bit slower
than 10m/min.

>If you'd like to test the issues I have with the Suunto, do a couple of
>dives on nitrox at a ppo2 OF 1.4 and 1.5 and compare them to the same dives
>one on tables.  If you decide to do this, please let us know how it turns
>out.

PPO2 of Nitrox 32 at 33m is pretty much 1.4.  And since Suuntos calculate
the PPO2 (and MOD etc) as if the mix was actually 32.9, it was running at
over 1.4.

Cheers,
Huw
--
http://www.huwporter.com