Posted by tleemay on February 21, 2001 at 15:26:59:
In Reply to: Aha! posted by Eins on February 21, 2001 at 13:03:32:
To the sport diver, how much bouncing up and down
is really bouncing. How much of a swing during
a dive? 10', 20', 50', 100'+?.
The point is that when planning a dive you plan
for your max depth and calculate you profile
accordingly. Your max depth the bottom "benchmark"
of your dive, the total extreme. If you plan for
and calculate that depth as part of your plan,
then any minor ups and downs (like 10-20') are
already figured into your profile. If during the
plan you exceed the depths and times, you re-
calculate on the fly how much you would add to
each stop, and even add a stop if necessary.
I think we all agree that the theories used in
the algorythims are just that. In theory they
should safely calculate any up and down you make
that saw toothed dive. Problem is that most
computers will penalize you and cut short your
bottom time or increase your stop depths and
times. There is also a difference amongst computers
in general, especially when comparing older to
newer ones. Some are more or less conservative than
the next one.
People are quick to start spouting off about
which algorithim their computer uses and will
follow it to the n'th pixel nust because that
pixel isn't in the yellow or red. Something to
keep in mind is;
The Buhlmann ZHL-16A was a algorithum generated
for theoretical use only. It was not designed to
be a set for divers to actually use across all
body types and diving styles. The Buhlmann
ZHL-16B was intended for divers to generate tables
and is widely used as a model for other table
publishers. The Buhlmann ZHL-16C algorithim
was designed with a skosh more conservatism built
into it compared to the ZLH-16B and is predominately
used in most current sport computers that do not
use the VPB or other named alorithim.
And as Michael has already pointed out, most of
these computers don't take into account deeper
stops and 3rd party gas like He - and try to
penalize you further.
Sawtooth diving, especially extreme bounces, is
hard on your body and tissues without some decent
length of off gassing in between. I'm not speaking
about dives where you go from 10 to 30 to 20 to
50 to etc while lobster hunting. I'm talking about
dropping to 130 and then up to 20 and then down
to 80 and back up to 50 and then down to 110, etc -
Depth swings that are more differential. If your
are a trained and practicing trimix or even an
experienced tech nitrox diver, or God forbid a
regular practicing deep air diver, these ideals
were brought up in your training and you should be
well versed in the physiology of pressure changes
on the body that constantly swing shallo to deep
without pressure breaks, that is surface time. The
edema the body tissues take with the constant
swelling and contracting of the tissues, plus what
the bubbles are doing while trying to off gass and
then being forced back to pressure can lead to other
complications that could impact the point of
taking a hit.
Diving with a planned schedule and knowing the
adjustments on the fly coupled with a complete
understanding of what it is your body is doing
while at that pressure and working rate is much
safer that relying on an algoritim and hopping
what it's telling you is in direct relation to
what depths, times, and workloads you have been
doing underwater. With a firm plan and associated
safety margins built in and contigency plans should
bottom depths or times be extended, relying on a
computer isn't needed.
Come to the DIR Demo when JJ get's out here and
you can ask him your questions and have him explain
how it works in person. He's the man - period. You
want to argue DIR for CA diving, here's your chance
- no excuses. Michael and John are right, explaing
what and how here is proving to be a waste of time,
and I have given it many hundreds of hours of my time
in the last 2+ years. The constant parsing of language
and "verbal gymnastic" (copyright 2000 MHK) has even
caused me to become defensive when I'm approached on
this particular issue. Apparently unlike most on this BBS,
we are out there most every weekend using no computer
and calculating on the fly for any contigencies.
We all bought computers in the past (well, most of us)
in our diving careers. Some have moved on realizing
a more cost effective and safer way in the long run.
I am not an expert on tables and decompression theories,
but I can say I know how to keep from getting bent
and continue to dive without a computer being my
diving "recess monitor" telling me when to come out
of the water... my dive plans are just better laid out
and with just as much bottom time and fun as others,
perhaps more.