Michiel,

There are some interesting problems with foam-in-place core (i.e. why do
you think Boston Whaler is almost alone in this.) The local pressures
that the expanding foam can cause can be significant. I have used
expanded in place urethane foam for several different purposes and it is
not as easy to work with as you might expect.

Think about the job you just proposed. . . .
You are going to have to do almost everything that the vacuum job
requires and you will still have to support the inner surface somehow
during the operation. And, now you have to patch the fill holes you put
in the weather deck.

If you are going to cut the deck open from inside. (The only advantage
this has is saving the non-skid molded into the surface.) Just put
core back in - plastic or balsa is little different - I find the balsa
to bind better to the epoxy, but places with lots of holes might want
plastic. Do Not use plywood at all. It has an inherent capaability to
migrate moisure along the grain. Balsa core is all end grain and
plastic? I did use plywood in some places of one job I wanted more
stiffess - the difference was not noticable from balsa - and have had to
replace some of it already.

It takes at lease 8lb core to be the same stiffess as balsa. The core
is the center of a beam structure. If you do not get the minimum
stiffness there, the beam will not be stiff. Plastic core is way more
expensive than balsa, but this comes back to the job cost/value
discussion that you need to decide.

Is this enough answer?

Matt Colie


Michiel wrote:
On Fri, 25 Nov 2005 11:54:18 -0500, Matt Colie
wrote:


Michiel,
Glad to be of assistance.
The responses are in-line.


(instructions for replacing the core with vacuum bagging)

Ouch.. that's more then I'm ready to take on now, in terms of work,
skill and supplies. I can see the point being made about the amount of
work.

Maybe yet another option:

I came across a web site that showed a pourable urethane foam:
http://www.shopmaninc.com/foam.html

How about cutting out the inner skin, scraping out the balsa core,
glassing the inner skin back in place and then pouring in that
urethane foam through holes in the outer skin? That 8lbs foam might be
perfect for it. I wonder what the viscosity is like.

Michiel