Re: concrete weight

[protek@shreve.net]

Jon,
    Did you consider the end caps also in your "slightly buoyant"
calculation?  Here is the problem; if you take a ratio of hull thickness to
outside diameter that you feel you can live with and it only produces a
"Slight" buoyancy then you have a major problem.  You have to fill this
hull with hundreds or thousands of pounds of system components.  This
requires the hull diameter to be gigantic.  Its a little like a business
that buys an item for $1000 and sells it for $1010 with a ten dollar
profit.  Can you imagine the volume you would have to move to make a living?
    Jon, someone wrote me and said they were thinking about a concrete sub
kit.  It would consist of a 3-foot diameter concrete pipe and two bird
baths to be glued to the ends (glue is provided).
    The foam you were talking about is called Syntactic Foam.  I am not
sure of the spelling as usual, but it is "Very" expensive.  It does consist
of glass beads in a resin matrix.  There are companies that sell the mix,
to mix your own, or they will make your shapes for you by specs.  I have
talked to them.  This foam is rated by depth in meters.  There is one other
buoyancy solution similar to foam that I am not sure has been expressed on
the site.  They make small "Spheres" that are 2 or 3 inches in diameter.
These spheres can be used to fill a vacant flooded compartment or they can
be glued together with epoxy to maintain a shape.  I think they are rated
to 300 meters, but I am not sure about that figure.  I have thought of
getting some to fill unused areas on my sub for extra payload carrying
capacity.  If I introduce one more system to my sub I may have to loose
weight one way or another.

Gary Boucher

At 01:42 AM 3/21/99 -0500, you wrote:
>I think I found what I was looking for.
>
>Dave Irons said;
>>"That would depend on the diameter of the hull
>>A slightly buoyant submersible would could have a hull thickness of . 08 the
>>outside diameter of the hull.  Example.  A five foot diameter hull = 4.8
inch
>>hull thickness.  A two meter diameter hull = 16 cm.  Most of the pressure
>>hulls studied were slightly buoyant.  Most were thinner than . 08 so the
numbers
>are
>>a little conservative."
>
>"slightly buoyant" Is good news for a underwater habitat because it won't
take much
>to hold it under water.
>But I think a sub hull needs to be more than "slightly buoyant" or you
will have to
>add some other form of  non compressible buoyant material to help carry
the payload
>weight. This is the case with Alvin and some other "overweight" deep
diving subs
>that use a non compressible foam to add to their buoyancy. I think it is
glass
>micro bubbles in a resin. I'll bet that stuff is not cheep. Any body know
about or
>use this foam?
>
>Jon Shawl
>
>