Newsgroups: rec.scuba
Subject: Re: Information about advanced deep diving course
From: wall@hel4.brl.mil (Jeff Wall)
Date: 9 Sep 92 13:10:01 EST
Distribution: world
Organization: U.S. Army Human Engineering Lab  Aberdeen, MD

In article <pjman5@twilight.wpd.sgi.com> story@sgi.com (David (Duis) Story)
writes:
>In article <1992Sep3.093029.3880@desire.wright.edu> wall@hel4.brl.mil (Jeff
Wall) writes:
>>
>>I've got a question that has been bothering me since I started hanging out at
>>the local dive shop which just happens to be a PADI store.  This dive shop
>>sells the Sherwood Source (a.k.a Oceanic Datamax) and I am under tthe
>>impression it uses the DSAT model. I this correct???
>>
>>If this is correct how do they figure decompression??  I know for a fact
(just
>>about everybody I dive with uses the Source) that the Source will allow a 
>>diver a 40ft deco stop.  So, if the Source uses the DSAT model then it is
>>theoretically possible ( if PADI were so inclined) to do deco diving on the
>>PADI RDP.  Yes???  No???
>
>No.  The RDP is not a full implementation of the DSAT model.  DO NOT
>use the RDP for decompression diving, or for repetitive diving limited
>by slower compartments.  Here's why.
>
>The DSAT model includes 80 and 120 minute compartments (albeit with
>not-very-conservative M-values).  The RDP *does not*.  That is, the
>exposures allowed by the RDP have been tuned to allow the table to
>(almost) ignore the slower compartments, instead using the 60-minute
>compartment to control offgassing.  That's why you get longer bottom
>times on repetitive dives using the PADI RDP than on the US Navy
>tables: DSAT assumes you're offgassing faster than the US Navy does.
>
>In fact, the RDP is not strictly a fully compliant implementation of
>the underlying DSAT model.  You'll notice that the RDP includes some
>"band-aid rules" to cover long repetitive dives which bring into play
>the slower compartments.  These "WXYZ" rules lengthen minimum surface
>intervals to allow the slower compartments to offgas appropriately
>after these model-pushing dives.
>
>In fact, Ray Rogers gave me a profile which is legal under the table,
>but breaks the underlying model.  You'd be hard-pressed to run into
>this profile in real life, as it involves about 2 hours underwater out
>of every 3 hours for almost a full day.  

This could almost be possible on Blackbeards (from what I've heard).

>The point is that the RDP does not take into account all the
>implications of the slower compartments, so if you're doing "extreme"
>exposures, including decompression and repetitive very long no-stop
>bottom times, you may be pushing close to the model limits.

So what you are saying is that the DSAT model is as good as any other model, it
is the implementation of that model in the form of the RDP that causes the
controversy.

I don't know anything about the full blown DSAT model although from what is
stated above it is a full decompression model and there really isn't any
problem using it as the algorithm in a computer.  I was under the previous
impression that the algorithms in these computers (Source & Datamax) was
closely related to the RDP when in reality they're vastly different due to the
manipulations described above.

Gosh, I'm so proud of myself, I didn't degrade the PADI Recreational Dive
Planner once. :-) :-)

Jeff Wall
wall@hel4.brl.mil

Newsgroups: rec.scuba