... The end
grain isolates moisture instead of wicking it the full length of the
structure.


Maxprop wrote:
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.

Yes, but "eventually" Mt Everest will be reduced to beach
sand, too. The progression of rot is much much slower with
end grain core than encapsulated plywood. I would not call
that failure, myself.


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,

Guess it depends on how you define "a lot" and what kind of
abrasion you expose it to. Fiberglass will basically have
almost no wear at all from foot traffic. Teak will... I know
this for a fact, having just removed a 20 year old teak deck.

BTW this teak deck was screwed into balsa core, which had a
dessert-plate sized spots of rot. If it had been plywood, it
would all have gone to mush.

.... which makes
the best non-skid of all IMO.

Disagree, but then that's based on personal experience
rather than heeding the opinions of others. Heresy!


.... For those boats with ply decks, many
manufacturers covered the decks with canvas and later Dynel or fiberglass.


I've read the Dynel is supposed to be better, not used it
myself.


.... 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.

The older Pacific Seacrafts, sure. The last ones I looked at
(2003 & 2004 models) they had deliberately built the boat
with glued-in molding & fabric liners so that you could not
see or access any part of the structure. Frustrating... and
suspicious IMHO.

I should have asked first... you know Pacific Seacraft was
bought up by a conglomerate? Personally I think they're
playing the sausage game. Nothing stays good for long.


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.


They might not have thought it made that much difference,
and couldn't afford the labor to do it right anyway.



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.

That's a good point. If the hardware is a lot larger, or has
at least 3 mounting holes, it's probably just fine. I was
thinking of single bolt stuff.

I also drill out areas and fill with epoxy to mount small
stuff with self-tapping screws.


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.


Interesting to see what the results will be. Airex and
Divinycell and Klegecell and there some new German stuff
that's supposed to be miraculous but is tediously expensive
are all less supject to compression failure, and certainly
less prone to rot but they are still not strong enough
to have rigging components thru-bolted to it. It may be that
the caulk is resilient enough to keep it watertight anyway,
in your application.

If you're interested, I can recommend some fairly technical
books on composite aircraft construction, which is what I've
been studying because there aren't any books on fancy
composite boat construction. Same stuff, same issues, though.


..... 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.


I used to use 5200 for everything, and then of course had to
peel/scrape/wirebrush it off, very tedious. Now I use
4200. And I own stock in 3M.....




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 . . .?")


Maybe it is pedantry, but my belief is that it's less work
to do things the right way. Especially if you don't want it
to fail at an inconvenient time.

Another of my theories is that 'if it works, it must have
been done right.' I'd like to see some of Frank's work & learn.

Fresh Breezes- Doug King