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Hi Les,
Welcome aboard, I live across the ditch in NZ, so
we are on a similar time zone.
I'm building a very small 1 person fiber glass
submarine out of epoxy, fiberglass & steel.
There's no weight advantage to be had in going
fiberglass or carbon fiber. You in fact make a heavier boat.
Although carbon fiber is stronger
for a given weight than steel, you need to go something like 4x the
thickness
to achieve the same strength. So if you have two
subs, one of steel & one of carbon fiber, with an identical internal
space;
the one of carbon fiber will be larger, displacing
more water & require more weight to sink it. You would have the expense
of
carbon fiber & extra lead as well. Another way
of looking at the weight issue is, if you have a 200 liter drum it's got to
weigh
200 kilos to sink, wether its made of lead steel or
polystyrene. The only way to get the weight down is to make it
smaller.
Carbon fiber is good in tension but I don't believe
its any better than epoxy / fiberglass in compression.
Round forms are the most pressure resistant &
just about all subs stick to cylindrical, spherical & conical shapes wich
put
mainly compressive forces on the material.
Being finer fibers its harder to get a resin to fiber bond with carbon fiber.
Steel has uniform strength in all directions but
fiberglasses don't. If you pull them in the direction of the fibers they're
strong, but if you
pull them diagonally to the fiber
direction they're not. You need to lay up in a way to compensate for
this.
There was a good article on why not to use
fiberglass in the psubs FAQ section but I couldn't find it.
I'm using fiberglass because I'm going very
small, it suites my design / construction technique & I'm prepared to over
compensate with thickness.
I'm aiming for the 250-300ft range.
The size of the dome you mentioned would mean the
diameter of your sub would require you to go quite thick with the carbon
fiber.
To get to 300ft with a dome 5ft in diameter you'd
need about a 45mm thick cast dome & I would hate to even guess at
what it would cost you,
Someone else might wade in with a guess.
Getting the Stachiw book on acrylic is a must. I held off buying it but am glad
I did. 1000 pages
all about acrylic. If you join psubs the discount
on the book that you'll get pretty well pays for your membership.
Here is a link to a free pressure program; you have
to download the sequel server first. You can also download the manual. It
analyzes cylinders
cones, hemispheres & spheres under external
pressure & gives crush depths, displacement etc. It doesn't show where ribs
should go.
A great tool for getting a rough idea of what
thickness material is needed for someone designing there own sub.
How many people is this for?
Regards Alan
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