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  #1  
Old 09-11-2010
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Moisture tester woes

I use my moisture tester (the eleophysics model Sail dog recommends) on a Tanzer 26 1975.
The deck did not seem soft when walked on but the meter was pegged to over 30 in many places. I'm pretty sure I was using the meter properly. The deck was not wet. I got a low reading on areas that are seldom wet such as cabin sides. I got a high reading in all the areas typically wet such as by stanchions. I tried a neighbor boat and it red bone dry.
I did not use a hammer but the owner said someone tapped it for him and said it was OK.
I have tested several boats and most boats that test over 30 are noticeable spongy under foot. This one is not.
I can't think of what I could have done wrong. Is it possible that the Tanzer is just made with a heavy enough top skin that even with a soaked core it is not soft to the foot?
The boat sank last year in fresh water. I'm wondering if enough moisture is trapped between the headliner and the cabin top. If that is the issue it should be moldy but I slept a night in it, with the hatch open, and did not notice a problem.

What do you think is the real situation?
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Old 09-11-2010
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It sounds the same as my CS27. Even when wet the decks are not spongy or soft because the liner and deck are both 1/4" thick. I have confirmed this with my meter (Electrophysics) and the areas I know to be wet are solid as the dry areas. I don't think tapping would work well for the same thick skin reason. That is probably the case with the Tanzer as well - when tapped it showed ok. I have no personal experience with a Tanzer but they are a well built boat from what I have heard.
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Old 09-11-2010
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Sandwich with soaked, wet core is not spongy. Delaminated, rotted core may be spongy or may not, depending on the fiberglass thickness and other supports of the area. Same with taping. Taping can find delaminated, rotted, hollow spots, however it doesn't show wet or dry core.

Technically speaking, core may be delaminated but still dry. It is often a case with foam core in high stress areas. Taping wll sound dull in such areas, however misture meter will show dry area. Opposite is often true too - balsa core can be wet but still structurally sound.
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Old 09-12-2010
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Quote:
Originally Posted by davidpm View Post
....... The boat sank last year in fresh water ....
What do you think is the real situation?
You don't need a meter for this one.
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Old 09-12-2010
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Quote:
Originally Posted by Minnewaska View Post
You don't need a meter for this one.

An intact fiberglass sandwich should not absorb water should it?
What are you saying?
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Old 09-12-2010
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Quote:
Originally Posted by davidpm View Post
I use my moisture tester (the eleophysics model Sail dog recommends) on a Tanzer 26 1975.
The deck did not seem soft when walked on but the meter was pegged to over 30 in many places. I'm pretty sure I was using the meter properly. The deck was not wet. I got a low reading on areas that are seldom wet such as cabin sides. I got a high reading in all the areas typically wet such as by stanchions. I tried a neighbor boat and it red bone dry.
I did not use a hammer but the owner said someone tapped it for him and said it was OK.
I have tested several boats and most boats that test over 30 are noticeable spongy under foot. This one is not.
I can't think of what I could have done wrong. Is it possible that the Tanzer is just made with a heavy enough top skin that even with a soaked core it is not soft to the foot?
The boat sank last year in fresh water. I'm wondering if enough moisture is trapped between the headliner and the cabin top. If that is the issue it should be moldy but I slept a night in it, with the hatch open, and did not notice a problem.

What do you think is the real situation?
A reading of 30 is NOT always mush and the skins will NOT always appear mushy. It can take a long time for the balsa to delam and rot. A reading of 30 is a good indicator that you may eventually have problems. A meter should always be used with spot soundings BEFORE determining any course of action. Before any glass work an actual core sample is also a great idea. If this is on the newish end of a 30 reading, meaning recently wet, the balsa may even appear as new.
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Old 09-12-2010
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An intact fiberglass sandwich should not absorb water should it?
What are you saying?
If the boat sank the sandwich IS and WILL be wet. Any screw or bolt penetration is a source for leak especially from the interior which is and should NEVER be sealed with bedding compound. Put that sandwich under pressure below water and it will absorb moisture quite quickly..
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Old 09-12-2010
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Oh no this make more sense than I care to admit. So what do I tell my friend.
The boat sank and absorbed moisture throughout the core. Every winter it will freeze and delaminate a little bit more.

So effectively this boat is effectively ruined as far as reliable structural integrety goes. Coastal sail for a few years until the inevitable delamination makes the whole thing too springy even for that.

This is worse than the normal rot around the chainplates and bow plupit because you can, with a great deal of labor, cut out the glass, replace the wood and reglue the glass. But in this case the damage is anywhere and everywhere. A sunk boat is for all practical purposes a dead boat.

Did I get this right.
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Old 09-12-2010
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David, if it has a wet deck core that has not broken down yet...In theory there should be some way to dry it out and reseal it. Offhand I'd hate to think of checkboarding both sides of the deck with 1/4" holes, sealing up the cabin with heaters in it for a month, and then resealing the (presumably now dry) deck afterwards.

But unless someone has a better way, I'd guess something that extensive might be required to save the boat. Slightly less epxensive than peeling the headliner and recoring the entire deck, perhaps.
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If the deck is very wet I don't think holes, however many, will dry it out. A complete recore is probably required.
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