Re: [PSUBS-MAILIST] Drive shaft alignment & sopport.

["Walter Starck" <wstarck@ozemail.com.au>]

Gary,

I do confess the comment you so object to was a bit tongue in cheek to
see if you would bite.  If you wish to take it seriously however it is
not entirely BS.  Certainly engineers do make possible much truly superb
technology but this does not obviate abundant examples of  poor
engineering involving needlessly complicated ways of doing things and
failing to take advantage of  readily available well proven solutions.

As for reliability of the thru hull cable fitting I described your
concerns are justified on the basis of not trusting your life to info
posted on the internet by parties unknown.  However what I have claimed
is easily verified by test.  You seem to be saying though, that you only
trust theory not the results of empirical experience. If so this is a
novel view of engineering as much if not most of  that discipline is
based on empirical knowledge not theory.  For the most part we really
don't truly know why things work but just that they do.  If on the other
hand, what you are referring to as theory is just the principles and
formulas which  quantify  our empirical knowledge please do apply them
to the problem at hand.  The parameters are simple, force, coefficient
of friction, and modulus of elasticity.   I have stated what I have
found from experience.  You imply theory does not support this.  I would
be genuinely interested in learning what theory, how it differs, and
what safe limits it predicts.

Walter Starck
Golden Dolphin Video CD Magazine
The premiere publication of diving and the ocean world.
www.goldendolphin.com






----- Original Message -----
From: "Gary R. Boucher" <engineer@sport.rr.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, November 23, 2002 12:01 AM
Subject: Re: [PSUBS-MAILIST] Drive shaft alignment & sopport.


>
> Starck Wrote:
>
> >If you enjoy problems and complicated expensive solutions complete
with
> >all sorts of reasons why what works in practice is no good in theory
and
> >should be ignored consult an engineer..  They can  solve problems
that
> >don't even exist and create new ones no one else has encountered
before.
>
> That is absolute B.S.  No matter what your profession is, you find
those
> who are incompetent, unknowing, and irrelevant.  The engineering
profession
> is no exception.  However, what I have found through the years over
and
> over is people who have limited knowledge of technical issues who make
> broad-ranging and very verbal assumptions.  These people, because they
do
> not completely understand the underlying theory, believe that those
who do
> understand and can employ that theory are somehow living in their own
world
> using tools that are irrelevant to good design practice.
>
> I will give a case in point.  I know someone that pressure chamber
tested a
> submersible window design using Lexan.  The window was one-time tested
to
> beyond the rated operating depth of the sub.  The Lexan actually had a
> noticable bow inward under pressure creating a convex/concave window.
The
> logic here was simple and of course not needing any real theory,
certainly
> not any engineering expertise.  The logic simply put was that, if the
> window did not fail under one cycle of pressure, somewhat over the
rated
> operating depth of the sub, coupled with the fact that Lexan seemed a
> wonder material and would never actually break, everything was fine.
This
> is a typical assumption made by someone that does not understand the
> properties of the material.  "No engineering theory needed here.  We
just
> proved that it will work.  We built 100 of them and never had a
problem."
>
> There is NO way I want to go down below very shallow depths in a sub
with
> thin Lexan windows.  Likewise, there is NO way I want to go down to
1000
> feet in a sub that uses wire penetraters made from flair fittings and
> O-Rings relying on nothing but the wire's insulation to keep the water
out.
>
> You do not have to be an "engineer" to construct a safe submersible,
if you
> find outside help from qualified individuals, but the PSUBer has the
> responsibility to determine who to get advice from.  After many years
of
> this type of work, I feel that I have just about reached the level
where I
> know what I don't understand and where to get good help.  Basically, I
am
> NOT an expert.  But, I know where to find good advice.
>
> Gary Boucher