I've never seen any older boat with a wood core in the deck remain dry;
not
even the end-grain balsa cores.

I have.

And it's not an issue of "even" the end-grain balsa.
End-grain balsa has several advantages as core. It's light.
The end grain forms a very good bond to fiberglass without a
lot of fuss, fancy materials, or careful workmanship
(although it's much better if these are applied). The end
grain isolates moisture instead of wicking it the full
length of the structure.

As for plywood "core" what's the point? Why not get plywood
that's strong enough in the first place, instead of adding a
skin of something that is heavier & not as resilient & will
trap water in the wood? Actually, the one exception is the
upper face of a deck. Fiberglass is a lot more abrasion
resistant than wood, and makes a great deck surface.


... A friend's Tartan 34 is so wet over the
forepeak that it squishes when walked upon. Irwins are no worse than
others
in this regard, but the glasswork and layup quality just isn't in the same
league as more expensive boats.


Well, any fiberglass lay-up with core that is not kept
sealed will end up squishy, no matter what the original
workmanship.

This is why some people hate cored fiberglass.

"Frank Boettcher" wrote...
As a sample of one, my experience has been that if a manufacturer puts
fasteners into the core without going all the way through, you are
much more likely to get core rot.

Pretty much guaranteed IMHO if that fitting has any stress
at all on it.

... I repaired quite a bit of it and
found it all related to that practice. I had a hatch cowl, head
ventilator, several escutcheon plates, and some others which were all
caulk and screw into the core. All eventually resulted in core rot.
When I repaired it I converted all of those to through bolt.

Ummm, I hate to tell you this, but that's actually worse for
cored lay-ups.

Balsa core is not very strong in compression. Actually,
neither is plywood, but it's stronger than balsa. When you
tighten the bolts, you compress the core. When the fitting
is loaded, the core compresses further (think stantion base
plate) and then when the load is removed, it doesn't expand
again (or at least, not 100%). Now the bolts are very
slightly loose. Repeat. Now water is guaranteed to be let in.

Frank I am very glad to hear you have not had any rot in
your core since making your repair. But that isn't the
textbook method and it's not any more work to do it that way.

The answer to this problem is to not have any core in the
area of fittings.

The original builder, if putting in core in the first place,
should cut the core to a template around all fittings, and
taper the core down all edges so that the two skins come
together and can be reinforced easily in the area of highly
loaded fittings. Ideally the edgees should have a double
radius, S-curve.

Look at a Morris, Oyster, or Baltic, and you will see this.
Look at an Ericson and you will see core with a flat taper
or bevel in the decks. Some eras of C&C did this as well,
but they also put in plywood or milled PVC blanks in place
too for some models in some eras. So did some other
builders. But many builders just toss the core in the mold
and slap cloth over it.


Maxprop wrote:
Damned if I can recall what manufacturer did this, but I recall seeing a
boat on which all thru-bolts were first drilled oversize, then filled with
solid resin--epoxy, I presume--and then redrilled to the proper, smaller
diameter.

The problem with this method of repair is that you're
cutting away the strength memeber... the skin. But the epoxy
filler is stronger in compression than the core, so that's good.

One method to dig out the core & leave the skin is to take
an Allen wrench and put it in your drill, and work it around
the edges of the existing hole. Put tape under, fill with
epoxy (I use hi density filler mixed in), then drill out the
original sized bolt hole.


.... No way any moisture could get into the core with that system.

It still can if the fitting is not bedded properly. That's
why the answer is to have solid glass in the area of fittings.

.... I
have Airex foam cores in my hull and deck, but I still do the same thing if
installing something. It makes for a lot of work, but it's a safe system.
I also overdrill holes into the core through just one laminate (snaps, for
example) and fill them with epoxy, too. Probably overkill in my case, since
Airex won't absorb moisture at all.


No, but freeze-thaw cycles will still cause progressive
delamination if any water gets into it. And Airex is also
weak in compression, thru-bolts will crush it and cause leaks.

Cored laminations are a higher level of technology than
solid glass. They're lighter, stiffer, more elastic, can be
engineered to have all kinds of desirable properties. People
who say "I hate cored fiberglass" are saying "I want my boat
to be heavier, weaker, slower, and less stable."

But cores aren't foolproof, they're not even user-friendly.
The real killer of cored structure is lack of maintenance.
How long has it been since all deck fittiings were rebedded?
Going on 2 1/2 years for me, and I'm thinking about doing it
again. But then I was raised in the old school where you do
this *every* year.

This turned out to be really long, sorry about that. But
it's an important issue. This should have come under the
"projects" thread earlier.

Fresh Breezes- Doug King