Sheet core-cell can easily be bent to the kind of curve you describe.
If it's obstinate, some kerfs cut on the table saw will do the trick. Apply
kerf-side up so they can fe filled later with light bog.
Bond the sheet down with epoxy-microspere slurry.
If the sequence of your construction will be to re-build the deck from the
bottom skin up, one way to provide higher-strength patches for the
attachment of loaded hardware would be to cut windows in the foam where you
want said patches to be, then after the foam's bonded down, fill the windows
with high-strength (like Cabosil) filler (Use slow hardener or they'll
exotherm badly. ), sand flush, apply the top skin and Bob's your uncle.
Just remember where the patches are.

. If it's
wrote in message
ps.com...
I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan