Shortcut for replacing plywood core?

I have a Rhodes 22 sailboat with some plywood core in the bow that turned to
mush. Water entered through a poorly sealed hole for a cowl. Last October I
scraped out the rotted core using wire. I was able to do this from the
existing cowl hole. The core I now need to replace extends about 1 foot back
& 180 degrees from the edge of the cowl opening. Ideally I would push in
epoxy with filler to fill the void but can't see an effective way of doing
that & repair such a large area. Then I thought about how handy it would be
to use an expanding foam to fill this area & then seal the edge with epoxy
at the cowl. The deck is very strong & does not flex. I don't think my foam
idea is a smart thing to do but I thought I would ask your opinion before I
abandoned the idea entirely. Any thoughts on fixing this without cutting
some fiberglass skin would be appreciated though I do have excellant access
to the damaged area from inside the boat.
Thanks
Marc

"Marc Beroz" <kfiske RemoveThis @erols.com> wrote in message news:<403f37af$0$3088$61fed72c@news.rcn.com>...
 > I have a Rhodes 22 sailboat with some plywood core in the bow that turned to
 > mush. Water entered through a poorly sealed hole for a cowl. Last October I
 > scraped out the rotted core using wire. I was able to do this from the
 > existing cowl hole. The core I now need to replace extends about 1 foot back
 > & 180 degrees from the edge of the cowl opening. Ideally I would push in
 > epoxy with filler to fill the void but can't see an effective way of doing
 > that & repair such a large area. Then I thought about how handy it would be
 > to use an expanding foam to fill this area & then seal the edge with epoxy
 > at the cowl. The deck is very strong & does not flex. I don't think my foam
 > idea is a smart thing to do but I thought I would ask your opinion before I
 > abandoned the idea entirely. Any thoughts on fixing this without cutting
 > some fiberglass skin would be appreciated though I do have excellant access
 > to the damaged area from inside the boat.
 > Thanks
 > Marc

Hey Marc,
It sure was nice of "OLD NICK" to give out such good advice for free!

Here's what I understand of your situation: 2 layers of fiberglass,
1/2 to 3/4 inch of mush in between them for diameter of approx. 2
sqft. and you have access to this mush through a small (6in.max)hole
in the middle once you removed the cowl.

The "right" way to fix this would be to rip off the top fiberglass
skin and expose all of the rotten plywood, then replace the core
material and apply a new fiberglass skin, then re gelcoat the whole
thing recreating the antislip patern on the deck somewhere during the
process.

I suspect that this may not be the best solution for you for whatever
reason. A 22 ft sailboat with a cabin trunk does not have a very
large fordeck,and does not have a large unsupported area.

So lets look at the the desired outcome before we go straight to
fixes. You want to replace the core with as little effort as possible
and still have a safe boat. The core simply seperates the two layers
of f/g to make for a stiffer panel section. To do this, the core
needs to be VERY WELL bonded to both top and bottom skins.
If your deck feels stiff with the mush inside, it's probably fairly
well build (or at lease the top layer is fairly thick).

Using 2 part polyurathane foam is an accepted practice in boat
building, especially by power boat builders. They tend to use 2 part
P/U foam to do everything from filling holes and deadair space to
bonding (non structual- eg: fish wells) items to the boat. This stuff
sticks to anything and is just as dense as cheap end-grain balsa core
- which is used in most boat decks built post 1975ish.

I would suggest that you go ahead and try the 2 part P/U foam but with
these precautions: get ALL of the rotten wood out, throughly clean the
area between the skins with acetone (3+ times), mix very small batches
of foam and let it expand and dry before applying the next batch(this
stuff expands so much that it WILL push the 2 layers of f/g apart if
it is trapped. once all of the foam is in, router out (or cut
manually) about 3/4 of an inch back from the opening where you filled
and replace with thickened epoxy. Give yourself enough room so that
the screws that keep the cowl on bite into the epoxy rather than the
foam.

IMPORTANT things to remember:
1. Get all of the "soft" wood out
2. clean throughly with acetone
3. mix small batches
4. let each batch cure before applying next batch(make sure you get it
into all of the corners
5. seal all edges with epoxy (just like wood, the foam will absorb
water, so keep it dry at all cost
6. Spend more of your time on the water

Cheers
R.<!-- ~MESSAGE_AFTER~ -->