Chiseled in Stone (Or Concrete)...

[protek@shreve.net]

Psubbers,
    I am often concerned about the safety of those on here.  I think
everyone knows that I do not endorse all materials for sub
construction, although in theory many could be used, but I seriously
question the wisdom of their use for numerous reasons.  Concrete is
one of those materials that I seriously question for use in a sub. 
However, I am not as worried about anyone getting killed in a
concrete sub, mainly because I feel that nobody is going to build one
to that stage of completion.
    Lets think about some facts here.  To build a concrete sub I can
only think of three methods one could use.  First, you could construct
a steel wire frame with wire mesh and apply the concrete on like
plaster.  This would result in hideous flaws, severe weak spots, bad
out of round conditions etc.  This would be an extremely dangerous
approach to say the least.
    Second, you could construct each part separately.  A cylinder, end
caps, conning tower, etc etc.  But this approach would be extremely
time consuming and would result in a bunch of concrete parts that
could not possibly be "stuck" together with cement to hold in the
environment to which they would be subjected.  Some form of
rubber gaskets would probably need to be employed.  But, how do
you bolt them or fasten them together.  Are you going to use a big O-
ring at each joint?  The latest that I have heard on here is that now
you cannot use rebar???  I don't know.  But, you will have to pull all
these parts together somehow, and I cannot think of a safe way to
do that, or even an effective way.
    The third method would be to pour the hull, end caps, and conning
tower in one pouring.  Now, this would be by far the best approach
from a seamless standpoint.  However, keep in mind that you will
have to build an inside hull out of something to form the inside.  The
outside will have to be contained by a second hull.  How are you
going to support a sub inside a sub when pouring, steel bars
(through hulls)?  Also remember the density of liquid concrete.  The
hydrostatic pressure is high for only a foot or two of depth.    Your
forms will have to be substantial!  How are you going to be sure that
you have all the air bubbles out of the mold?  What happens if you do
have an air bubble?  Plaster over it?  What about inside the hull wall
itself?  X-ray it?
    Supposing you used method-3.  Once you got your hull finished
the outside would come off easily I assume, but what about how you
would get the inside form out?  I think it was proposed to use wood
for the inside forms, I think it was for the beauty of ceder or
something like that.  How do you remove the wood??  Do termites
eat cedar?  What about African Termites, can you import them for
the job?  Just a little joke here, chill Rick...  Nothing personal.
    Being as I have built my own fully functional sub and taken it
down a number of times I would like to give some insight into what
you are probably going to feel if you do build a sub and test it.  You
are going to wake up in the middle of the night and start thinking
about what could go wrong that you have not thought of yet.  You
are going to question each and every one of your decisions.  If you
are using a material like concrete, you will wonder about it before,
during, and hopefully after the dive.  It is not a choice that I could
ever be at ease with even if I made 50 dives in such a sub.  There are
many unknowns centering around the material itself used in this
type of application.
    I will also share something you may not have thought of, or
realized at this stage.  The actual hull construction is NOT the
majority of the work.  On my sub it was probably less than 25% of
the total work I performed.  The bulk of your time will be spent on
window systems, ballast systems, electrical systems, pneumatic
systems, the hatch system, the propulsion system, the steering
systems, and numerous other entities not mentioned here.  It is a
common misconception that the hull is the majority of everything
and if a hull could just be constructed, the rest will be easy and fast.
    I worked off and on with my boat for years.  I think I could build a
steel hull if I had the parts on-hand in a month or less.  The concrete
idea seams like it would be cheeper.  I personally think it will raise
the cost by a factor of 3 or 4.  With steel you just weld in your
through hulls fittings.  Concrete; not so easy.  Everything has to have
a special interface.  Windows; can't weld them to concrete.  You
need a mounting system, and one that does not compromise the
concrete.  Almost every system will be made more complex using
this approach.
    I think that the main reason people want to try different materials
is that they do not feel comfortable welding or don't really know
how.  You will save money, time, and rest easier overall if you hire a
competent professional to do the welding if you are not skilled
sufficiently in this area.