Join Date: Jul 2015
Location: Northshore of Huron
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Re: HELP, mushy plywood under bow chainplate
Paint us a picture of the underside of the bow where the bolts for your stemhead (the chainplate attachment at the bow) go through the deck. If the underside of the deck looks like fiberglass with the bolts coming through and nuts on them then we are talking deck core that is rotted and not just a backing plate as mentioned earlier. A backing plate would not be sandwiched into the deck, it would be exposed.
The issue with rotted core in a structural area like this is that it's meant to bear the upwards pulling force from the forestay. That force is supported by the nuts on the bottom of the stemhead bolts, and then to the underside fiberglass layer, then through the core, and to the top layers you see on the deck. If the core is rotten then you essentially only have the 1 thin layer of underside glass supporting those nuts\washers. They could pull through would be your worst case, and since we are talking forestay here, would most liklely result in a dismasting.
Yes the forward edge of the stem head is bolted to the bow, and should be strong, however the bolts on the deck are there for a reason and weren't put there just for looks. It's not often production boat builders added extra parts\work without reason.
You won't need to pluck the mast most likely, as long as you can secure it with a halyard or two as far forward as possible. When I changed the stemhead on my Mirage 33 I used the main jib haly and spin haly to support my mast. I ran them as far forward on the toe rail as I could (about 6" short of where my forestay attached) and winched them up tight. The mast never moved. I would not rely on a single halyard to hold it, but that's just me being extra cautious. If you are in a rolly marina, and are already in the water, and your fix may take a few days to do, you may consider plucking the mast.
Some youtube videos, nothing fancy
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