Thanks for your comments. I've responded to some of your points below.

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.

That's correct. The core is 1/2" plywood.

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 figured if I removed a fiberglass skin, it would be the inner one since I
have good access & I wouldn't have to deal with the non-skid. This leads me
to another question if I go this route. In one area the mush core has been
removed all the way to the edge of the deck. To replace this core, how close
to the hull/deck joint should I cut the fiberglass skin? If I cut too close
to where the deck meets the hull, I won't have enough space to grind out a
bevel & then reglass the skin back into place. On the other hand, the
further out from the hull I stay with my cut, the harder it will be to get a
good bond between the new core I install & the inner fiberglass skin that I
did not cut out along the edge of the hull. (I'm having a hard time
describing this.) I've been mulling this over for awhile & been been
thinking I'd cut the deck's lower fiberglass skin about 2.5 inches away
from the hull. Any thoughts?


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.

The only reason I was looking for an alternative is that I want to minimize
down time. I was looking to make the quickest repair without sacrificing
safety. I thought that if I made a foam repair & that failed, I could always
do the traditional repair at some point in the future.


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)

I assume you get the acetone in there by shooting it in with a syringe &
then allowing it to evaporate out?

, 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.

I've looked at the foam products & have wondered how I could get 2 part foam
back far enough between the skins. Is there any way to spray it rather than
pour it? Or are you thinking that I close off the cowl hole in the inner
skin and then pour 2 part foam in from above the deck. I don't have
experience with 2 part foam. Is it real viscous prior to setting up or will
it flow? What if I used 1 part spray foam?

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.

Agree

IMPORTANT things to remember:
1. Get all of the "soft" wood out

I can get all the soft stuff out that I can move with a 1/16 inch diameter
piece of wire but that won't be as good as having good access to the problem
area with a skin removed.

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


The more I consider the obstacles, the more I think I may just have to bite
the bullet & get to work cutting glass. I'd be interested in what you think.
Thanks, Marc