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

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

Gary,

On hydraulic propulsion I do think it falls in the category of
unnecessary complexity and expense with a performance penalty as well..
As for your engineering judgement outside this I know nothing and have
no opinion. My comments on over engineering were generic to a commonly
encountered circumstance not a judgement directed at any individual.

On the matter of the thru hull cable fitting your concerns seem to be
based on a rubber insulated cable.  This is the type I specifically
advised against.  The type I did recommend has a solid PVC outer
insulation.  PVC is not only much stronger it slowly cold flows where
compressed by the O-rings.  This locks it into place very securely.  The
50 lbs. extrusion force mentioned in the example is far below  what it
will withstand.  Nothing you have offered in the way of theoretical
dissent contradicts this and it is easily tested.  This is beginning to
look like an example of the NIH factor.

NIH is often the impetus to coming up with complicated solutions and
ignoring simple proven ones that are already available.  NIH is short
for Not Invented Here.

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 10:35 AM
Subject: Re: [PSUBS-MAILIST] Drive shaft alignment & sopport.


>
> >Gary,
>
> Starck wrote:
>
> >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.
>
> You're actual tongue and cheek, yet not entirely BS comment, is held
by a
> number of people I have met.  One close friend feels that I am the
only
> engineer he has any respect for.  He can't stand all the others.  The
> fellow does superb work and is the best craftsman I have even known as
he
> builds aircraft from the ground up.  These are not kit planes, he does
> extensive modifications of existing high-performance planes and
constructs
> some of his own designs.  I have a great deal of respect for his
mechanical
> judgement, yet there is an element missing.  He never calculates
> anything.  He shoots from the hip and it may someday get him in
trouble.
>
> You apparently, because of my use of hydraulics, feel that I am a
person
> that applies needlessly complicated approaches to simple problems.  I
will
> let my work stand for itself.
>
> >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.
>
> Your posting on the Internet has nothing at all to do with my
unwillingness
> to adopt your method for deep water thru-hull penetration.  Your
> credentials have nothing to do with it either.  If you had a doctorate
in
> mechanical engineering with extensive work in the field, that would
not
> mater to me either in this case.  I will let your note continue.
>
> >You seem to be saying though, that you only trust theory not the
results
> >of empirical experience.
>
> If you knew me better you would not even suggest such.  I am a strong
> believer in empirical experience and judgement.  Much of my work is
based
> on intuition.  I know when to go with intuition and I know when to
shift to
> hard numbers.  No one I know and no body that works with me thinks of
me as
> a theoretical engineer.
>
> >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.
>
> You seem to be trying to parse my reasoning into two categories.  One
> practical and the other theoretical.
>
> >   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.
>
>      Part of my profession is teaching physics at the university
> level.  Almost every day I deal with factors such as force,
coefficients of
> friction, and Young's Modulus.  All the problems work out so nicely on
the
> board.  All the numbers agree to three decimal places with the answers
in
> the back of the book.  It would give the student the impression that
> everything in physics is just so precise.  But, the truth is far from
> this.  Translating pure theory to practice in the real world is not so
> one-to-one as a person might think.  These factors are good for
predicting
> estimates and ranges of expected performance, but often fall way short
> because the simple parameters do not exactly match or there is or can
be
> many factors too complex to accurately estimate.
>      In the case of the wire mentioned in an earlier post (0.40 inches
in
> diameter) the load calculated was 55 pounds.  That means that the
wire's
> insulation, not the wire itself must be able to take a compressive
load of
> this value.  Should there be any exceptions in any of the parameters
or
> just a flaw in the wire's insulation itself, failure could easily push
> uninsulated wire through a hole intended for the  insulated wire's
diameter.
>      I can run numbers on the O-ring penetration using estimates for
> coefficient of friction and the like.  But my person intuition, my
> engineering intuition, my knowledge of how such parameters vary in
real
> live tells me to not get in that sub at that depth.  You are simply
making
> a jacket of rubber into a pressure bearing structural component.
>
>      If you want a good example of rubber failure consider how many
> unwanted births are caused by some component made of similar material
> failing when it is supposed to hold up under the rated load!
>
> Gary Boucher
>
>
>
>
>
>
>
> Let me state just a few, but I am sure, not all of the not so simple
factors.
>
> Coefficient of friction varies greatly with age of a material,
lubrication,
> moisture content etc.  Wire insulation properties also vary with age
and
> conditions.  Given the example of a 0.4 diameter wire I used in a
previous
> post, the loading on the insulation is about 44 pounds per lineal
> inch.  Assuming a "Wet" coefficient of friction for rubber against
O-Ring
> of 0.6 the loading will be around 73 pounds per lineal inch.
>      O-Rings are not intended for
>
>
>
>
> >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
>
>