Re: [PSUBS-MAILIST] sub

["Captain Nemo" <vulcania@interpac.net>]

Sarah,

Your idea is a novel one.  Here's a few numbers.

A six foot sphere displaces about 7,232# of sea water (more or less,
depending on which variables you use in your calculations); i.e., that's the
buoyancy potential of a structure that size and shape.

If that sphere were made of 1/2 inch mild steel, it would weigh about 2,260
lbs.; that's 1130 lbs in 1/4 inch; and 847 lbs in 3/16th.  Figured on the
half-inch hull, you've got about five thousand pounds of "stuff" you can add
to the design (ballast water included) before she'll submerge at neutral
buoyancy.  That's a lot of extra stuff.

If you make the hull out of acrylic, it's probably going to be thicker than
that, so if you're leaving yourself about 6-feet inside, the displacement is
going to be more, and the amount of compensating weight you'll need to
include will be more,also.

Not saying a round sub can't be done.  Back in '65, the Johnson brothers of
Texas built a submarine from a 6-foot steel cable float, and it worked
nicely to depths of about 100 feet.  Might have gone deeper, but as far as I
know that's as deep as they took it.

The sphere is, of course, the best shape for withstanding depth pressure
stress; but it's not well adapted for low hydrodynamic drag in motion.
That's why most hulls are a combination of round and elongated: the best of
both worlds.

If I understand you correctly, you want to stand inside this hull and roll
around on the seabed by walking in it?  If that's your goal, I'd stay away
from acryllic, which would be scratched and gouged in no time, possibly to
the point of structural failure.

But why do you want to "walk" (roll) around on the bottom, when you can
"fly"?  Submarines float; that's the beauty of their mobility.  I'm not
saying it can't be done, but it just isn't a good way to go.  What if you
roll into a bed of silt?  That big ol' ball is gonna get stuck tight, and
generate a lot of even suction; easily too much to overcome. And when I
consider the possible effect of currents, I see this concept as requiring a
lot of superhuman physical effort; when if you did things a little
differently, you could simply sit comfortably and drive around.

If I were going to build a round hulled sub, I'd rig it to operate in a
basically upright attitude, and maneuver via external electric motors.  And
that's what I'd suggest you try.  Considering the variable between weight
and buoyancy of even a half-inch hull, you'd certainly have enough residual
buoyancy capability to carry everything you wanted to bring along!

Hope this helps.

Pat