Bob,
Be very careful with this. If you use polyurethane expanding foam, it is NOT
closed cell and it will eventually absorb liquids. When it does, it is very
hard work to remove. This kind of foam is very valuable on a steel boat
because of condensation and rust. If you insist on using the stuff, you use
a sealing paint for insurance. Styrofoam is good enough for your purpose, it
is easy to both cut and glue and it doesnot absorb moisture.
Steve

"Bob La Londe" wrote in message
...
Ok, I'm in the middle of a rebuild/repair on an aluminum boat. I just
jerked the plywood sole out of it in order to replace it with aluminum
decking, and I found what looks like plant arranging foam between the ribs
for flotation. It soure doesn't look or feel like a sealed cell foam.
Its also quite a bit narrower than the space available. I was thinking
about replacing it with foam that fits snug between the ribs to increase
the flotation slightly, but I'ld like to use the best thing possible.
Would styrofoam be more suitable? I know styro hardly absorbs any water
at all. It lasts indefinitely as the flotation under docks as long as its
not exposed to sunlight. .

How about a poured foam? Are there any that form sealed cells as it
hardens? Would it work here, or would it be too hard to get it level with
the ribs so I can put in the new sole? I'm not sure I want poured foam in
here anyway, as any water that comes in the forward deck hatches etc drain
through the strength creases in the hull to the back of the boat where it
can get kicked out by the bilge pump.

I'm thinking if I can styro that its just the right thickness it will be
the best foam replacement, but there is a lot more experience in this
group than I have.

Bob La Londe
www.YumaBassMan.com