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Well....
Not to be picky, but I did suggest a couple of coats of fibreglass
(FRP). I have used this technique in making motorcycle fairings, and it
is very strong. The foam just acts as a free-form mold while the FRP
hardens. Once the outside shell is formed, the foam is removed. For a
fully enclosed shape, removing the foam would be difficult without
compromising the structure (you would need a hole).
What I haven't calculated is:
1) How thick would the FRP have to be to withstand
X psi at depth?
2) How heavy would it be?
3) Would exotic materials (Kevlar) be required?
3) Could it really satisfy all the requirements WRT
-size
-drag
-flotation
-extra weight
-safety
And I am looking through my #%*)@!! Pocket Ref (2nd edition) only to
find it doesn't list the density of styrofoam. But, I know it is lower
that 32lb/cu.ft. Another material used in boat-making is Balsa wood
(8lb/cu.ft.). Too many dependancies in fibre:resin ratios and types,
but you could ballpark at 120lb/cu.ft. For 20 lbs lift, whole structure
would weigh in at 6-10lbs depending on shape and a lot of other things.
More disclaimer: The above figures were based on a big pile of educated
assumptions. Guess-work is no substitute for luck:)
ttfn
David Pearson
In message "Rigid Foam Flotation", doug@su*.su*.ne* writes:
>As already mentioned styrofoam will crush under pressure. Case in point
I
>have made great shot "glasses" from styrofoam cups by putting a few in
a
>mesh bag and sending them down with oceanographic sampling instruments.
>High quality cups make nice dense symmetric shot glasses (about 1/3
size);
>poor quality are substantially distorted. Styrofoam plates are hard to
eat
>from due to their thinness after pressure treating. Of course this was
a few
>years ago before I realized styrofoam was the work of the devil!
>
>Try contacting Kelegecell or Divinicell for rigid closed-cell PVC foam
sheets
>which will be able to withstand the pressure. 'Or if you would like to
mold
>the form, Flotation Technologies makes 5gallon kits of syntactic foam
(epoxy
>type matrix with tiny glass spheres for flotation). I have (2) 6" x 12"
x 12"
>extremely high quality syntactic foam blocks (apx. 32 lb/cu.ft) ($900
list)
>which I will give away for $100 plus shipping?
>
>Doug Chapman
>
>--
>Send mail for the `techdiver' mailing list to `techdiver@terra.net'.
>Send subscription/archive requests to `techdiver-request@terra.net'.
>
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