Plywood knee rot question - SailNet Community
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post #1 of 16 Old 12-01-2010 Thread Starter
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Plywood knee rot question

The way our boat was blocked on the stands this winter has allowed water to drip in on the backstay's chain plate knee (it's sealed now). This knee is 90% encapsulated with fiberglass except two spots right were the dripping has been (past month). Unfortunately, this has soaked the wood in this area.

Would the marine plywood have any chance of still being OK if properly dried out, or will I have to cut this out and reglass in a new knee? I drilled a weep hole in the bottom, but not sure if I can do anything else without causing more damage.

How can I tell if this wood is rotten? I probed the area that I drilled with an awl, and it was hard, but wet.

Thank you,

Matt

1989 Sabre 34II Targa
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post #2 of 16 Old 12-01-2010
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If the water didn't freeze and damage the wood...you might be okay. Personally, I'd replace it and fully encapsulate the new knee... losing your backstay could end up being very expensive.

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post #3 of 16 Old 12-01-2010 Thread Starter
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I was more hoping for something along the lines of "just let it dry out and it will be fine", but I expected the actual response.

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Matt

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post #4 of 16 Old 12-01-2010
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as a retired shipwright i second the opinion always better to repair properly the first time more expensive to do it hap hazard then replace when it fails. winter is a good time to do it. then its done right and ready come relaunch time.

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post #5 of 16 Old 12-01-2010
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I will go against the grain here. If it has only been wet a month or so I would dry the plywood out and inspect it. If it is still firm and looks just like dry plywood I would not worry about it. If it has rotted it will be easy to spot but that does not usually happen that quickly.
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post #6 of 16 Old 12-01-2010
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my reasoning for replacement is based on the assumption that this is not a brand new boat which means more likely than not the ply has been wet before and considering the cost to replace it now verses the cost to replace everything if the worst is to happen. (Murphy's law if it can fail it will at the least convenient time.)

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post #7 of 16 Old 12-02-2010
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That was my reasoning too, combined with the fact that the weather in Michigan has been below freezing long enough for any absorbed water to freeze and that can cause serious damage that is difficult to inspect for if it is deeper into the knee.

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post #8 of 16 Old 12-02-2010
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I am not understanding how blocking the boat could be the sole factor in the leak and would think it was leaking much longer ?

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post #9 of 16 Old 12-02-2010
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I agree with dog - replace it and be done with it. But use g10 and not plywood and never worry about it again.

Brian
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post #10 of 16 Old 12-02-2010 Thread Starter
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It's not the cost that is a concern (to a point), but more getting it replaced properly. I'll be doing the job, and after building a dinghy a few year ago, I have a pretty good handle on fiberglassing, but I'm still worried about completing a structural repair this important. Besides the missing glass on the top, the rest of the fiberglass work around this part is a thing of beauty.

Please tell me this is as easy as cutting a new knee and normal fiberglassing!

Typically, the boat sits with the deck angeled aft. Unfortunately, when it was blocked, the boat was leveled on the deck. This caused the scuppers to be in a position that allowed the water to puddle on deck. This puddling was large enough to drip in an area that wasn't water tight. This is the first year that it's being stored outside in the elements.

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