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At 10:52 AM 12/10/99 -0500, you wrote:
>Doug, cut the crap, If you are going to talk about real dives you have to do
>real dives. If you chose to begin counting your bottom when you step on the
>boat, that's fine with me. If you want to use PADI OW rules for your diving
>that's fine, too. If you chose to use an air computer for your dives and
>wait out the computer so it won't beep at you all day, that is fine also.
>
> You don't even have anecdotal evidence to the contrary. I have evidence
>that it works. Try it sometime-EZ
>
First of all Eric, you have no clue as to what kind of diving I do, and
quite frankly I could care less how you define a "real" dive. Read my post
again especially the words about "generally recognized decompression
theories" that define bottom time as the time from the surface, to the time
of the beginning of the ascent. This specification is the basis for almost
every recreational dive table - do you disagree? As far as "anecdotal
evidence", its not necessary because there are volumes of published
literature in this regard.
As my post also illustrated, the gas uptake can be incrementally calculated
on descent which I assume is what you are eluding to, although without any
explanation on your part. I think we would both agree that including the
descent time in the "bottom" time would be prohibitive for deeper dives.
However, in not doing so it should eventually be considered somewhere. This
is readily accomplished by incrementally calculating the gas uptake during
the descent in a table generation program to derive the initial gas loading
conditions at the beginning of the actual time on the bottom. These methods
are discussed in depth by Workman, Buhlmann, Brown, et.al. Again there is
no need for anecdotal evidence because you can readily find published
literature on the subject.
I suppose we could include statistical methods like maximum likelihood. I
suspect the decompression procedures developed by WKPP also include
statistical assumptions. If so please illuminate - I'm interested.
As a note I don't use PADI OW rules for my decompression calculations. I
use custom software that doesn't include all the mystery margins and bells
and whistles. I apply the safety margins as I see fit. Thus far this
software has proven acceptable to near 500ft with a reasonable
decompression profile and generous deep stops; and yes it doesn't include
the descent time as time on the bottom.
I am not a fan of the word "PERIOD" as the absolute final truth in
anything. H2Ocaver in making that statement was wrong because for the vast
majority of divers (using tables), bottom time means from the surface to
the beginning of the ascent. This doesn't necessarily mean its the best
way, or the only way, but just one way. For deeper dives, IMHO it is
prohibitive as I already mentioned.
I'm not going to get into a pissing contest with you (or anyone else) on
this subject; however if you wish to discuss something relevant I am all
ears. Unfortunately all I see 99% of the time on this (and the Cavers) list
is alot of "I have evidence that it works. Try it sometime" without any
detailed explanation and scientific or statistical basis. Without that it
sums up to being next to worthless, because I learned a long time ago not
to do things just because someone told me it was OK. If I did that I'd be
dead ten times over. If you are a scientist or engineer you would
understand that. So if you have something to share, do it. What's (or was)
your major at USF?
-Doug
P.S. A note for Chris W. (H2Ocaver) - don't associate me with USDCT. I base
my decisions of fact, not fiction.
>
>
>
>>H2Ocaver wrote:
>>>2)Bottom time starts when you hit the bottom and ends when you leave the
>>bottom PERIOD.
>>
>>Pretty certain ("PERIOD")??? But wrong! Even your most basic PADI course
>>instructs that bottom time is the time you leave the surface to the time
>>you start an uninterrupted ascent to your first stop. If it becomes
>>interrupted, then it becomes multi-level. Following generally recognized
>>decompression theories (e.g. Buhlmann, Workman - the basis for many tables
>>and computer programs) you will find their guidelines for constructing dive
>>tables define bottom time in the same way. They also define an ascent rate
>>which figures into the inert gas loading for computing an empirical
>>decompression. It depends on how you wish to solve the differential
>>equations (Workman has solved for a changing gradient on descent, but I
>>believe the tables based on his work lump descent time with bottom time as
>>well). Sure, there may be some statistical methods that may wish to define
>>bottom time differently, but it would be interesting to understand how to
>>account for descent time without solving or accounting for incremental gas
>>loading during the descent or lumping it into the time on the bottom (for
>>simplicity and margin). Case in point: On a 400ft dive, you take 4 minutes
>>to make your descent, and then do a 20 minute time on the bottom. Are you
>>saying the 4 minutes should be ignored and only the 20 minutes considerd?
>>Not in my program. Gas loading is a function of a gradient and time of
>>exposure, regardless of the type of gas. Hey I'm open for hearing relevant
>>information about new and improved decompression theories.
>>
>>Take care,
>>Doug
>>
>>
>>
>>
>>--
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>
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