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

["Gary R. Boucher" <engineer@sport.rr.com>]

>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