Re: Public response to J. Shawl

[Phil Nuytten <72020.572@compuserve.com>]

Subbers:
        I noted, with some interest, Rick Lucertini's eloquent response to
J. Shawl's comments ( where Mr Shawl appeared to be implying that there
were some parties advocating research/'odd' materials/innovative design 
etc. -  over safety):
 
Mr. Shawl says > "it is discouraging to me personally when some-one goes
and says you can build a sub out of anything that keeps out water"   Well.
goodness gracious . . of course you can!! That statement was not meant as
my opinion - it is a simple statement of fact! You could make a perfectly
adequate submarine ( "sub" ="under/below" and "marine'"="the ocean/sea")
out of rubber - it just wouldn't go very deep and would take a lot of
weight  to get it under -  but if you were content to be at ambient
pressure and wanted high portability . . .etc.,etc. I gave the subbers
credit for understanding that the most basic  material/geometry choices
always exist and do so in an almost bewildering profusion  of alternatives
- it was not my intent to discourage any-one - only to open up some of
those possibilities for discussion . . .which I assumed was one of the
major reasons for having a forum of this nature.
         A  major problem with getting too specific in the subject of
material selection/suitability/depth is that it requires a precise set of
parameters or definitions to be known, or agreed to, by all participants.
For example . .we talk about "mild steel" as a common sub material - what
we really should be saying (instead of 'mild') is : a steel with a yield
stress ( in Ksi) of 36.0000 Ksi -  a Young's modulus ( in Mpsi) of  30.0000
Mpsi - a Poisson ratio of  0.3000 - a density ( in lbs/cu in) of  0.2830
lbs/ cu in . We would then need to define, specifically,  what structure we
are talking about . . .say, a cylinder with 'adequately' capped ends , size
. .36 inches ID X 36.5 inches OD ( wall thickness= 0.2500 in ) X 60 inches
OA cylinder length ( disregarding heads).  If you asked a designer about
this configuration, the designer  could say " Sure, it will go into a
thin-wall collapse mode  at 0.1573 Ksi external pressure or a depth of
about 350 feet - and, using the 2:1 design collapse/safe working depth
ratio required by most  certifying agencies ( Lloyds/DNV/ABS etc.,) that
would give it a safe working depth of 175 feet.  It will weigh 483 lbs in
air and have a bouyancy of  1841 lbs. I could give you the specific Delta
stress for delta I D/ delta O D/ and delta length . . an so on"
        The above is not to be smart nor patronising - it is the most 
basic info required to make the most basic  calculation of safe depth . .
.NOW comes the harder stuff - you say you want to cut a hole in the centre
of this cylinder so you can get in? well, how do you propose to restore the
strength and intregrity  of the cylinder?- doubler plate? ring? You get the
idea. I'm sure.

        Some of the subbers who have built their own subs can tell others
how they did it . .what specific hull materials/dimensions/geometry worked
for them . . . and most seem quite willing to do so.    Some seem to
indicate that they have arrived at sacred grail through a torturous and
dangerous maze and tell others that they, too, must travel  that trail and
should listen well to avoid pitfalls. Nonsense. Basic external pressure
vessel design is little more than arithmetic and a grasp of exactly what it
is you are trying to do and how it usually accomplished. 
        If you just want to know how deep your favorite propane tank will
go, pay an engineer for a few hours of his time and quit screwing around!  
        If you are interested in this kind of stuff - go buy a copy of a
softback titled " Structures - or why things dont fall down" by J. E.
Gordon    ISBN  0-14-021961-7  and look at  'tension structures and
pressure vessels'  cost you about ten bucks . . .and I give you my personal
guarantee that you will get much more than ten bucks worth out of it !! And
if you like that, then try " The new science of strong materials - or why
you dont fall through the floor"  also by J. E. Gordon  ISBN 0-14-02.0920-4
( about $5.00) If you develop a taste for this sort of thing, there are
dozens of such books in your local library!
        I must thank Rick for valiantly riding to my rescue -  but it
really isn't required . . what is, is. My opinion has no more or less
validity than Jon's - that's what makes hores- races ! Actual facts are
something different than opinions, however, ( unless the facts and your
horse are one and the same! ) - and pseudo-facts, jumped conclusions,
narrow perspectives,and all that sort of stuff - are just  a waste of
everybody's time - IMHO

Phil Nuytten