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Dan Courtney
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Discussion Starter #1
I'm rebuilding a 1975 Reliance 44. I've gutted the interior and before I put in new cabinetry I checked the hull with a moisture meter. Turns out I have a spot around a through hull fitting (above the water line) of about 25 ft2 on starboard side with moisture readings ranging from about 30% to a peak of 59%. There is also a larger area (maybe 45 ft2) on the port side, also with similar moisture readings. The port side also seems to be emanating from a through hull fitting. Both through hulls will be replaced and re-sealed.

Question: What moisture level is "safe"? My meter reads "risk" for anything over 30%, but does that mean that anything over 30% will eventually rot?

Thanks.
 

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Is this a cored hull and if so what is the core?? If a solid glass hull the moisture readings are not a big thing but would certainly want to find out where the moisture is coming from and fix it. Sounds like the through hulls need to be R&R'd at a minimum.
 

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Dan Courtney
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Discussion Starter #3
should have mentioned that it's balsa core... about 1 inch thick. And yes, I'm going to replace and re-seal the through hulls.
 

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If you're rebuilding the boat...best to replace this wet core now. Its not going to get better if you wait. Even if you stop the leaks...the moisture is still there, and the rot will continue. There is nowhere for the water to go. I've got a cored hull too, unfortunately, and I'm over the top paranoid about it.

Ideally, there would be no exterior wood at all on a sailboat. Much less wood literally sandwiched into the structure of it where it can't be inspected!
 

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al brazzi
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Are the thru hulls in solid FG, should be I would think. If not I would fix that. Were they added later on and not done right? If you're gutted now I would think fixing from the inside would be easier but I will admit Im no expert.
 

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You may get lucky and find the core just wet but you'd have to be awfully lucky for that to be the case. You'll need to determine the condition of the core, replace it if it's rotten, dry it out if it's not. Others may have better ideas but using a hole saw to drill holes to find the extent of the wet core, condition and dry it out would be a start. Lot's on the net on how to replace the core. Nice boat but balsa core is a major problem if it gets wet and rots.
 

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美國佬
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621 Posts
I've come across a lot of very wet deck core on my boat, but very little of it has been rotten, and it's been wet for years. Not that having wet core is good or anything, but it doesn't necessarily rot right away. If you drill into it and the core comes out black and mushy, it's rotten.
 

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Dan Courtney
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Discussion Starter #9
Thanks for the input guys. I've done some reading since my post and found that at about 30% is when free water is available for bacterial/fungal growth. Free water plus oxygen is necessary for rot. So the core may or may not be rotting, but either way I need to either replace or dry it out. I don't know if the through hulls are original, but I suspect not since they're plastic. And they are through the core, although I haven't investigated to see if the core immediately around the hole was filled with epoxy or not.

I'll be jumping in to cut away small sections of the inner skin (so the hull doesn't deform sitting on the cradle) to expose the wet core. Wish me luck!
 

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Dan Courtney
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Discussion Starter #11
Boatpoker, Very interesting. I just pulled a 1 x 4 foot section of the inner skin off and re-measured the core. It was virtually identical to my original measurements with numbers ranging from 10 to 100. Most of the area had numbers over 30, so I removed that portion of the core. Surprisingly none of the core removed was wet to the touch. Even a spot that was a bit darker and measured 100 (I thought it must be mush) was dry. Some of the balsa seemed a bit spongy, but nothing felt wet. I thought maybe I was picking up the bottom paint on the exterior, but when I probed the plastic bag containing the core chunks I had just removed I got readings in the same range as when the core was in place. What the ....?

What's odd is that I've re-done much of the deck of this boat (also 1" balsa core) and the same meter very accurately predicted wet core. Anything over 30 was wet to the touch, and over 50 could have water easily squeezed out. But as the article you pointed me to says, a meter alone on a hull is pretty much meaningless. I guess I'll take a couple of core samples for my own peace of mind, and then tap the entire hull with a hammer to make sure it's solid. I think you may have saved me about three months of labor and a couple hundred dollars on materials. Thanks!
 

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Dan Courtney
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11 Posts
Discussion Starter #12
Boatpoker - I just realized that you wrote the article you pointed me to... very well done. So after cutting out a section on the edge of the area my meter said was "wet" I discovered that it was dry to the touch. So today I drilled a core sample in the center of the "wet" area (next to a through hull, and found that it was indeed wet to the touch. So I proceeded to drill 1/4" holes every 6 inches or so around the center of the area and physically sampled the core. There ends up being a 2 foot diameter area around the through hull that "feels" wet.

My question... if it feels dry (I squeeze the sample, and even press it to my lips to detect any hint of moisture... but get no sensation of moisture) is it below the magic 30% value? Am I safe to replace only the areas that "feel" wet, and leave what "feels" dry?

Thanks for your help.
 

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Wet is one thing, rotten is another. If it is just wet, drying out the wet area will probably suffice. The important thing is R&R'ing the through hulls so they are fitted in solid, not cored areas and stop the leak. The leak will eventually translate into rotten core and a must replace scenario. You can probably fill in the area around the through hulls with multiple laminates of glass and epoxy so the now uncured hull is thicker and stronger. More importantly, it will no longer leak moisture into the core if it should develop a leak in the future. Suspect current leaks is caused by compression and release of the cored hull around the through hull breaking down the seal with the part.
 

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Dan Courtney
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11 Posts
Discussion Starter #14
Thanks. For reasons I won't get into, it will be better to replace the wet core than to dry it out. There are actually two through hulls next to each other. One I will close up completely, and the other I will (as you suggest) set in solid epoxy. What exactly does "R&R" mean?
 

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Dan Courtney
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11 Posts
Discussion Starter #16
Oh... thanks. Although tecnically that would be R&R, R, R, R. But cutting it down makes you sound less like a pirate!
 

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al brazzi
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I have to wonder , knowing wooden Boats typically rot above the water line from fresh water intrusion and below the waterline in salt water is pickled pretty well, and preserved. Does this translate to cored hulls vs decks.
 

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Dan Courtney
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Discussion Starter #18
Albrazzi - good question. Although in my case the through hulls in question are above the water line. Also, one through hull was the output for the holding tank, and the wet balsa has the scent of sewer.
 

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How much wetness is too much?

If the boat is cored, then any noticeable moisture is too much. If the core is a 'botanic' material such as balsa; then doubly so, because 'wetness' immediately implies fungal intrusion and rot.

If the boat is solid FRG in structure and the laminate is wet, then IMO, a small core sample should be drilled into the hull etc. and that (solid) sample be sent to a 'mechanics laboratory' to be investigated and analyzed for 'hydrolysis', etc. - an analogue of rusting and ultimate 'break-up' of those long chain molecules in 'fiberglass' and other composite/'plastic' structure resulting in a chemical and structural degradation due to the contact with 'water' including water as a 'vapor/gas'.
 

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Dan Courtney
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Discussion Starter #20
RichH - it's balsa core. I understand that anything over 30% moisture content is considered "wet" and will eventually rot. I've drilled holes and pulled small samples of the core from the area. My questions is what does 30% moisture content feel like? Is it obviously wet, as in being able to squeeze water out of it? Or is the water locked up in the fibers so that it feels like it's dry?
 
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