After Rebedding Chainplates

[Lare]

When I'm done adding the sealant should I re-connect the shrouds right away or wait until it cures?

[Bill Schmidt]

Yes!
Billy Manana

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[Ian Macrae]

My thought is to reconnect right away. Applying pressure after it
cures might mean it would be too stiff to adapt to the new pressurized
position. Let it cure under pressure and in its final resting spot.
This question about when to tighten might be like the debate about
which is better, a Ford or a Chevy.....For trucks, obviously a Chevy
or GMC!

The workers just got done cutting out the two knees for my top and mid
shrouds, the port and starboard (obviously). Inside the fiberglass
"triangle" that is visible when you take the trim box off were two
wooden triangular pieces of 1/2" (or close to 1/2, I didn't actually
measure it) plywood. They weren't glued together, just held together
by the fiberglass and the chain plate bolts. It was obvious that
water had gotten into the wood, as there was rot and mold. Trying to
imagine the mechanism of the failure that allowed my deck to be pulled
up, I'm thinking that as the wood rotted it stopped giving structural
support and rigidity, and the load transferred to the fiberglass that
surrounded the now rotten wooden triangles. Then the fiberglass
started flexing and working which led to its disintegration. I have
to say that there was not really that much rot, but apparently enough
to cause the whole thing to fail. And before the failure it wasn't
obvious to me or my rigger (who had installed new shrouds in December)
that there was a problem. There were a few water stains around the
knees, but nothing that would cause alarm bells to go off. Even after
I found the deck pulling up, there was nothing really dramatic to see
around the fiberglass knees....a few little cracks and broken threads
of fiberglass and some separation of wood along the bulkhead and
underside of the deck area.

So, make sure you keep those little plates around your chain plates
well caulked at all times!

Ian

P40, Freyja, #49

[Larry Byers]

I finished the job today and connected and tuned the shrouds while the caulk was curing. That made the most sense to me.

Thanks for all the help everyone!

Lare
SV Rocinante
>

[Bill Schmidt]

Ian et al: I've said this before, many times before: The plywood is cheap,
construction grade plywood, not marine grade and only used as a form for
constructing the "real" knees made of fiberglass. The REAL problem is either
a Bob Perry design problem or a Wendell Rankin, builder problem, depending
upon who you want to believe, or both. Either way the problem is that the
fiberglass knee tears away from the hull. Perry states (lately) that the
design called for the knee to tab into/thru bolt into a bulkhead that Rankin
didn't use/build. We went to Tom Wiley, when this problem happened to Wind
Witch, for a separate redesign (and subsequent construction). He told us,
through the boat yard, that the problem was a design problem---something
that BP has had issue with for a long time. Compounding this revelation (or
whatever) has been that knees for the upper and middle shrouds were not
built systematically to the same specs. There were "long knees" and "short"
knees. The boats with "short knees" (which appear to be made on forms
really intended for the construction of the knees for the forward and aft
shroud chainplates) seem to be the ones that fail or have failed first. I am
not aware of any boat where the smaller knees forward and aft on the lower
shrouds have ever failed. They leak as often as any and, if rot were a
problem, I would think that we would have seen some of these being a problem
too.
There have been many different solutions used on boats over the years.
"Trial Run" has a stainless steel belly band running from port to starboard
attaching to the knees on both sides. The knees of Wind Witch are very long,
massively thick and fenestrated. They are made of S-fiber roving (whatever
that is) and have no voids for puddles. In 25 years, they have never leaked
nor needed rebedding except for when we replaced all the chain plates in
Mazatlan in 2006 when we redid the teak decks. On Wildflower (I think) the
problem was solved by attaching a turnbuckle to the chainplates and to a pad
built lower down on the hull, then taking up a tension. I am sure there are
other solutions used as well. God only knows which is best.
With regard to when to retension after rebedding, I really don't think
it matters. Those shrouds and chainplates flex and shake recurrently when
sailing and tacking. So long as you don't use a rigid cement or caulk, I
doubt it matters. Think of how many sailboats are constructed and how long
it usually is before they are finally fitted with a mast. Long time, long
time.

Billy Manana
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