Plywood core moisture levels

[AzoresGlide]

Hello everyone, newbie here.

Was wondering if there is a consensus regarding acceptable moisture levels in the plywood core areas of the deck and floors.

I found a Mac25 project boat with around 40% moisture levels in those areas, including under the mast base. For reference, the non-cored (solid) glass areas were showing 3%. It's also been sitting outside in Canadian winter with its usual freeze and thaw cycles.

That said, it's my top choice aside from a C&C Mega 30, which are much harder to come by. Can I squeeze a few more years out of it or should I move on? Should also note it has some trailer damage on the hull that has been bondoed over and will need repair.

[Wyb2]

My understanding is that the actual reading on a pinless moisture meter is not very meaningful. It’s not measuring moisture directly, it’s measuring capacitance. You really need to get some reference points on similar materials, so non-cored areas aren’t a great reference point. Some scrap dry plywood might be better if you can’t find an area of known dry core.

On my boat the deck would read anywhere from ~15% to pegging the meter. That was helpful because 15% became my reference point. I drilled exploratory holes, and was surprised to find even areas reading 90% seemed completely fine and the shavings weren’t noticeably wet. Some areas pegging the meter had rot around the hardware mounting holes.

[kenfyoozed]

I am in the process of replacing the core in my 26D. Unless the price is very attractive , ie free I would suggest to keep looking. I thought I had a good boat but it turns out not to be the case. It will be almost bullet proof when I’m done.

[Chumpy36]

I am in the process of replacing the core in my 26D. Unless the price is very attractive , ie free I would suggest to keep looking. I thought I had a good boat but it turns out not to be the case. It will be almost bullet proof when I’m done.

How are you doing it? Cutting from top or bottom? I have a couple soft spots. I replaced the rotted core near the mast base with synthetic material and it’s solid as a rock now. Will likely use that stuff again.

[kenfyoozed]

I am cutting from the top. I am leaving about 1-2" around the perimeter. I used a "chain saw" disc on a angle grinder to remove the core as far under the perimeter as I could. I will use a 1/2" Coosa under the tabs. It will be bedded with compound. Then a 1/4" Coosa layer will be added to bring the core lever with the original fiberglass. Finished up with at least 2 layers of dbm1708 or db170. Not sure if I will be using polyester or epoxy yet. I want to secure the core with epoxy but glass it over with poly, but epoxy is probably a better choice over all.


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[AzoresGlide]

Interesting, thanks everyone. I guess at this age every deck will be wet and it's just a matter of it not cracking.

An idea emerged to remove the mast, cover the fragile deck with solar panels, and fit a long shaft 1000w electric outboard, equivalent to 4hp.

This seems interesting because it should increase relative stability. Might get away with boating around with the swing keel up