Posted by seahunt on January 16, 2001 at 16:42:30:
In Reply to: Re: DIR on the West Coast posted by MHK on January 15, 2001 at 18:22:08:
When it comes to sport diving, it seems that DIR is a solution in
search of a problem, whether there is a problem or not and whether
DIR is the solution or not.
Hmmm. I didn't think I was that harsh in my response, but when
I was done, my hard drive crashed... luckily I keep a spare handy
at all times... NT though it be. So lets do this again and maybe
even make it more brief.
Oh, and by the way, it was on George Irvine's site that offered that
SPG placement was for reading while on a scooter.
*** (1) To continue...
As a minor point there may be a mis-understanding. I use a console.
I like them too. Compass on back, SPG and depth/computer on front. I think
that is what you are talking about... convenient and un-obtrusive.
A console has no noticable momentum and minimal drag. The only
time it has noticable drag is when it is hanging down during a swim in
the open. Then it can be put in the strap on the BC that is there for
the purpose (great in coral areas) or what I do is just throw it back
between my legs. It works great. Very easy. Much more convenient than
fixed to arm.
Please explain to me, in physical or engineering terms, how a console
on a hp hose bursts the DIR bubble and violates its highly developed
system. In engineering or performance terms, the DIR system can
certainly handle a small (possible) increase in drag from a console.
What is destroyed by that drag is an ideological vision of DIR, not
the physical or engineering performance.
You keep talking about coefficients of drag and how it increases
with cross section, but you miss that it is the velocity that makes
for a square of the increase in drag. Your whole system is missing
important engineering analysis. That is OK for some guys in their
cave, but to bring DIR more mainstream, you had better get some real
engineering analysis of the system. The old seat of the pants
experimental engineering methodology just doesn't cut it in the big
city. ..Then you have the arrogance to claim engineering perfection.
I really cannot figure out your fanatic dislike for consoles
when they are usually small, unobtrusive and very convenient. Even
if you don't like the minor trade off, many people do.
.. The hp hose is going to be a possible failure point whether it
goes to a SPG or a SPG in a console.
OK. Al vs Steel. Yes, you critisize my making contingency plans
but you ignore my point. An old arguement form the pseudo-Marxists
ideologists used to use against science based arguements. I have to
remember never to use the self critical forms that are the strength
of science. You will always turn the self critial part against me. So
I will make it simple.
I did over 1000 dives with steel tanks, some of them deep, before
BC's were invented. Many divers currently do the same, with no apparent
problems. My friend Lem uses a 140 cu ft tank with no BC. No problem. I
have had occasion to do a few fairly deep dives with a smashed
overpressure release. I had no problem.
An aluminum 80 is just not enough air for a good dive at any depth
and exertion. I even like a low pressure 95 steel better, but a steel
100 is just enough air and it is small and light.
I see no big problem to a steel tank and great advantage to them.
They are too convenient to leave behind because of a theoretical problem
that doesn't seem to occur in the real world.
People do it all the time. Just ask your friend Chris. He'll be
happy to tell you.
Doubles. Pardon if I call them silly, but I used to use them a lot
and found their size and inconvenience ridiculous.
Unless you swim at near the same attitude that you walk, your
doubles are not in a slipstream, they are above you plowing water. I
swim pretty level or even a bit head down, which puts the tanks in a
line above my head and shoulders. The drag is enormous even if I put
my head up. Any surge makes you rock like a boat on the surface. They
can be great deep, but bring them shallow and the surge makes them a
Then there is simple momentum. They may not weigh anything
underwater, but the momentum is the same. When hunting, I constantly
change direction, front and back as well as to either side. Everytime
I start or stop, I feel the momentum of the tanks.
Now back to the real sticker, computers.
It sounds like you are doing multi-level dive calculations with a
table, perhaps a wheel. In theory, you are using the same algorithms
as the computer. You must be doing a lot of depth and time
I'll look at this from a few points including safety, accuracy,
convenience and reality.
I use the tables fine for repetitive dives and have taught others to
use them as well. I could do my calculations underwater, but what a
hassle. Also, realize that regardless of training, there are many people
that could not do them. In any case, I have better things to do. I am
down there to hunt, photog or explore, not keep track of time and depth
and do calculations. If I am in a situation where a dive could go into
deco I know where it is before I go down. If before that, my computer
suddenly goes dead, I am not going to be in a deco situation. I will be
gone before that. There is no danger of computer failure putting me in a
The safety issue disposed of for the moment, consider that
computers are better at calculations than humans or we would be
still using slide rules.
I am quite capable of using any system of tables and algorithms
I want to learn, probably far better than most people. I have taught
people to use different tables on occasion. I am far better at doing
math calculations than most people and so I know the nature of making
single calculation errors as well as the built in error factors of
multiple calculations. Ask an accountant about that. They can tell you
what the studies say about error rates. That is their business. There
is always a predictable error rate. They will also tell you that a
computer is far more reliably accurate.
I'm considered by many to be good very good software developer.
My long experience has well taught me to not blame the machine for
errors. If there is an error, it is something I did, not the machine.
This does not mean that I am stupid or careless. I just make a lot of
decisions and I am human. To be human is to err.
As far as convenience, there is no comparison. During a dive with
a fairly constant depth, it would be an annoyance to manually do the
sampling and calculations. During my typically erratic multi-level dive
that I make, not only would accuracy be pretty much impossible (see
below), the constant sampling and calculation would consume all the dive
time and be a complete pain in the butt.
I'm not talking about cruising the Badlands of Nic or Talcot Shoal.
I'm talking bouncing up and down Eagles reef.
The terrain is against you. Along the islands, at the rigs and
probably more than 50% of the Channel Island diving, there is a huge
vertical component to the dive area as well as the horizontal
component. When sight seeing or hunting, you may be changing your depth
constantly. Human calculations just cannot keep up with my diving. If I
tried, it would take all of my attention and when I am hunting, I give
no attention to anything else that I don't have to.
Really, it comes down to the dive.
Could you make 7 dives in a day with a 95 steel with max depth of
129 feet and at least 70 feet on all other dives, in one day, using
tables? Do you think you would be able to sustain a reasonable accuracy
rate? Why take the risk?
Consider Gordo Banks. I made a dive to 165 feet and a dive to 150
feet, 45 minutes apart. I would feel much safer doing it with a
computer. My experience has taught me to rely on my instruments unless
I have reason to doubt them. It's just safer.
Here is a description of a typical profile for me lately. Please
tell me how you would evaluate it for decompression obligations.
I like to night dive at Eagles reef. Drop to 25 feet and look for
shallow bugs. Usually there are only shorts, so proceed clockwise around
to the wall and drop to the sand at 95 feet and quickly look for walkers or
if the bugs are deep. Continue to move along the wall up and down between 70
and 50 feet, looking for bugs from underneith. When I reach the shoulder,
move back onto the reef so that I have now circled past 180 degrees and am
moving up the other side of the reef. There are shelves at 50 and 30 feet. It's
a fair sized area to search. At the end of that, I will be back where I
started. Drop to 60 feet so that I am at the base of the rock wall that is in the
leading edge of the current. Move up it fast to look for bugs out in the
current. Repreat this about 4 times as I move around the rock. Then look
for a shallow ridge to wait out some ascent time.
Next dive is Isthmus High Spot. If I miss the top, as I usually do,
I am in 70 feet and the tables say I am almost done with the dive. Move down
to the edge of the sand at 95 feet and quickly look for walkers or others at the
reef edge. Head up the reef and look for the high spot. If I can find it, the
dive can be finished crawling under the elephant ear kelp at 60 feet, pushing
sea lions out of the way. If I don't find it, as usual, the rest of the dive
will be at 70 feet.
You want to take the time and distraction to try to calculate that?
You think you could do a better job than a computer? Really, I don't
think so. There is no better way to track that dive than a computer.
Think about a dive against the island, say the Rock Quarry. You have
a limited horizontal area along the shore to work. You have a vertical area
from the surface to the sand. Efficient searching of this area means a
complete range of depth along the length of the shore.
Think about the Rigs. My profile was deep to look, say 120. Look for
scallops at 70 to 50. Cruise up a bit to look at the ecological changes.
Too much air to go up, since it is a relaxed dive, so head back to 55 and
take pitures. Air is low, so move up to 20 feet where the mussels start and
hang out there taking pics until it is time to go.
Look at my site. Pick a dive I have written about where there is any
topography to work with. Tell me how you would profile the dives with a
Considering dives with a profile as erratic as mine, which are not
extrordinary, anyway you look at it, what a hassle to avoid carrying
something the size of a cigarette package.
After working through the ambiguity and dang near deceptiveness of
what I can find on the web about DIR, I can narrow down what looks to
me to be some of the issues as they relate to west coast diving and
especially hunting/photog. These include use of a console, steel tanks
with a wetsuit and use of a computer verses multi-level calculations.
There are other issues like a BC or a buddy, but they are passed over
here for fairly obvious reasons. I do reserve the right to come back to
them. I do believe that these first three issues are intentionally
obscured because they would prove so controvercial. If not intentionally,
it was still sure done well.
A console is a great convenience and has minimal drawbacks, mostly
minor drag... very minor. The most curious point of this is how this
can completely discombuberate the DIR system. I think that that is not
an engineering reality, but instead an ideological given. Trying to tell
me about how it messes up the flow of the system, but that doubles don't
increase drag is beyond my belief without a far better and more accurate
As for the issue of steel with a wetsuit making it difficult to reach
the surface in the case of not having a BC to help is ignored by the people
that do it as a regular thing. Hey, there's only about 5 or 6 pounds
The computer is the best thing for divers since scuba. Why not use
it? It's not a safety issue if it fails. Computers just do a better job
than humans of sampling and calculation. Plus, with my dive profiles,
manual sampling and calculation would take up most of my attention,
attention that I need elsewhere. By most ways of looking at it, using
a computer is also far safer. Besides, it's so much easier.
... Looking at the recent posts, some people say it's not important,
some otherwise. In any case, I find the computer fantastically useful,
convenient and safety enhancing. I will be interested in your future
essay on the subject.
As I said earlier, DIR seems like a good idea and with a bit of
adaptation it would be fine for sport diving on the west coast, but
the proponents of DIR say that is not possible. Well, I don't believe
it and I have carefully said why. It's funny that it is not the system
in question. It is the perception of the proponents of the system and
their contention that it is not an adaptable system.
In any case, enjoy the diving, seahunt
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