"DSK" wrote in message
...

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.

That was the theory behind end-grain balsa, but ultimately it didn't work.
Eventually the wood will tranfer water a great distance between lamina. It
may take quite a bit longer than with a ply core, but it will eventually
happen. A 25-30 year old balsa core will be fairly wet if exposed to water
at hardware attachment points.

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.

It's probably not a lot more abrasion resistant than dry teak, which makes
the best non-skid of all IMO. For those boats with ply decks, many
manufacturers covered the decks with canvas and later Dynel or fiberglass.

... 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.

Well built yachts generally have this feature, such as Pacific Seacraft.


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.

Those same builders never anticipated being in business years later when
those cores were soaking wet, either.

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.

You're cutting away such a small diameter of the skin that I think the
result is negligible, especially if the unit of hardware being installed is
quite a bit larger. Some craftsmen recommend using an angled piece of wire
to "route out the balsa core within a 1" radius or so around the hole, and
filling that with epoxy and microballoons. I've done this on other peoples'
boats, and it seemed to work reasonably well, too. This preserves the skin,
but I was always unsure if the epoxy was getting into the voids between the
glass laminates adequately. With my overdill method, I am assured the area
is completely resin-filled. That's why I switched.

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.

Hmmm, sounds familiar. See above. g



.... 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.

Agreed. That's why it's worthwhile to invest in quality boats--one's that
have this feature, for example.


.... 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.

It's surprisingly stiff and rigid. I installed a sheet stopper on the cabin
roof, and I was preparing to route out some of the Airex and replace it with
epoxy and West System's colloidal filler, but the local glass man told me it
wouldn't be necessary with Airex. I couldn't detect any undue compression
when I tightened the fasteners. Of course I bedded them and the stopper in
polysulfide caulk, tightened only slightly until the caulk had a chance to
set up slightly, then tightened it further.

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.

Then there's the school of thought that if you bed everything in
polyurethane (3M5200, for example) you'll never have to do it again. That's
true, because you'll never be *able* to do it again, and of course it will
leak with time. Terrible idea.


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.

I think some of us enjoy projects of this nature. And some of us are
pedantic enough to want to do it in the best possible technological manner.
Most owners are clueless. ("You mean you have to rebed those things? What
the hell . . .?")

Max