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Old 15-07-2010, 10:33   #1
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Boat Deck Moisture Readings ?

Hello,
To eveyone whose boat is in the water...bless you! To the other of us who are on the hard...help!! I've been taking the decks off my Sigma 41 this year...started with teak removal (which was screwed down) and filled the holes with epoxy. Then ground down the adhesive and stuff to the gel coat..and then took moisture readings with a Tramex Skipper Plus. Found high levels on the deck but not on the coach roof. The deck is cored with end-grain balsa. I had a fiberglass serviceman look at and determined there was moisture as well. I assume he was using something similar? I started peeling off the top sandwich and found some moisture, especially in the bow area and by the chainplates. Nothing was rotten but for the two front cleats. The further back from the bow the harder the skin was to remove and the dryer the balsa appeared. I've removed the top skin and balsa to about even with the main winches, leaving only about 4 feet of the deck not disturbed by me. I've replaced the core with honeycomb polypropelene and then three layers of bidirectional fabric and fiberglass cloth using AeroMarine epoxy. Originally I thought I could re-use the top panels that were removed but they seem as though they've got moisture in them according to the Tramex. I even went as far as cutting some of the panels and cooked them in my oven for an hour and didn't realize much moisture change.

Question, did the boats in the 80's (1984), use polyester resin which gives high moisture readings eventhough they're not wet? There were no spots on the deck that "sounded" with moisture but that's my analysis. I want to do everything properly as eventually I'd like to sell the boat and want the buyer to have a great boat. Thanks for reading this....
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Old 15-07-2010, 11:28   #2
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Greetings and welcome aboard the CF, projectgator.

Take comparison readings on sound hull areas.

See the Guide to using Tramex Moisture Meters on GRP
http://www.passionforpaint.co.uk/dow...ipperguide.pdf
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Old 15-07-2010, 11:37   #3
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We can assume you boat is layed up with ortho resin, which takes quite a while to release it's moisture (if at all). GordMay is correct, you need to "draw" averages of the known dry areas on your boat, then compare these with the moist ones.
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Old 15-07-2010, 11:53   #4
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Thanks, I've taken many readings as the boat has been out of the water since last fall, but is stored outside so rain, etc. continues to fall on it. Eventhough the soundings are solid, as long as the meter reads "wet", the fiberglass/core should be removed?
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Old 15-07-2010, 12:22   #5
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Quote:
Originally Posted by projectgator View Post
... Eventhough the soundings are solid, as long as the meter reads "wet", the fiberglass/core should be removed?
No.
Normally, I’d trust a “good” result from percussive sounding. “Bad” results are less persuasive.
Take moisture readings in a couple of areas where percussive soundings give good results. Open one up, and inspect to determine which test method is most accurate.
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Old 15-07-2010, 12:58   #6
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That's what I've been doing. It seems as though the moisture is in the fiberglass/gelcoat and less in the balsa core. The only moisture apparent is via the moisture meter. Nothing rings on the sounding or once the fiberglass has been peeled...Does that make sense? Or do I just continue to remove it all knowing the moisture will be gone? Thanks!
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Old 15-07-2010, 15:26   #7
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G'DAy PG,

If I'm reading your query correctly, you have replaced the balsa with honeycomb and then glassed over the new core. Now you are wanting to put back the upper layers of the old deck on top of the new glass, but are worried about the possible moisture content of that old glass.

It seems fairly unlikely that deck glass, not being submerged in normal usage, would have absorbed sufficient moisture to be worried about... especially when you have sealed up the new core material with epoxy.

My general impression is that interpreting the readings of "moisture meters" is a fairly subjective matter. To condem a isolated piece of laminate which can be inspected, dried and retested seems draconian.
I see little reason to not use the old skins if that is what you want to do.

By the way, I admire your ability to absorb punishment! A daunting job, indeed. Good onya, mate!

Cheers,

Jim and Ann s/v Insatiable II lying Manly, Qld, Oz where I'm struggling just painting the bloody decks!
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Old 17-07-2010, 15:18   #8
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I must have missed the portion of this thread where the new core and laminate additions have been done with epoxy. If this is the case then you can apply the old poly external skin right away. The epoxy will form a barrier to future moisture mitigation at the very least, assuming bonded fastener holes, etc.

Personally, I'd support a tent over the whole shooting match for a few weeks and insure you have dry decking, repair areas, etc. A big tarp isn't much money for the insurance it can bring to the project.
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Old 19-07-2010, 12:43   #9
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pics of my summer project...

Thanks for the words of encouragement. The panels in the first pic have been cut up and "cooked" in an oven but still harbor moisture according to the Tramex. BTW-cross sections of these and all panels shows no evidence of delamination...all solid..but moisture? I'll put on some current pics after next weekend which I hope will be my last application of fiberglass bi-axial cloth.
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Old 19-07-2010, 13:37   #10
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Some gelcoats use titanium dioxide as part of the coloring agent. Meters can read this and make it appear as moisture when it's not...
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Old 19-07-2010, 14:02   #11
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MORE PICS AND SUCH...

I did a quick google on the titaniuim oxide...it appears to have some deleterious effects as well. I've been using a dust mask and have removed most of the gel coat but I suppose I'm grinding some of it further into the fiberglass. Good to know this may have contributed to my elevated numbers. Thanks!
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Old 19-07-2010, 14:57   #12
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Sheeesh, quiet a repair job. Not sure I would have gone to these lengths but the worst is over now

The Sigma was built by the same folk (Marine Projects now Premier Yachts) that built my Moody so many of the fittings are the same. We caught the chainplates leaking but hopefully before any damage was done

What is holding the mast up in the last two photos btw?

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Old 19-07-2010, 15:18   #13
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chain plates pics...

Pete,
The mast is held up with great balance....it's a beautiful thing until it fails...actually mast is keel stepped so it's just tethered by the fore and aft stays....Here are some pics of the chain plates before and after. Original were very wet plywood that leaked into the cabin. I chiseled out the wet plywood until I got down to the last veneer and then epoxied two sheets of okuma plywood and then encapsulated them in fiberglass cloth/epoxy and then epoxied these into the chiseled out area, leaving an area where the double-chain plates enter the deck and cabin below. I epoxied this with coloidal silica and epoxy and will raise the final elevation of the top chain plate by about 1/4" above the deck to help prevent standing water from finding it's way down below.

Your boat has very simliar lines to the Sigma...I'd be curious to poke around the Moody to see how much transferred over...

I learned some years ago..if you're going to do it...you may as well do it right so you don't have to do it again...I hope I'm following this philosophy?
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Old 19-07-2010, 15:27   #14
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closer look..port chainplate

You can see the epoxy bed around the thoughdeck fitting..
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Old 19-07-2010, 16:21   #15
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Lol, never thought about a keel stepped mast

A look at Yachtsnet shows that because both Sigmas and Moodys were built along side each other, many of the components were sourced from the same suppliers. The woodwork cut from the same timber and ply, layup by the same craftsmen etc.

Moody 31 archive details - Yachtsnet Ltd. online UK yacht brokers - yacht brokerage and boat sales

I know linking to another forum is frounded upon, but I would like to make an exception on this occasion and draw your attention to the Moody Owners Association. The forum and the technical archives now have an impressive amount of advice on these boats, much of which will apply to Sigmas too. If you are stuck for a No2 metric, left handed widget, the answer could be here, MOA Home Page

There will be some movement between the deck and the chainplates. Rather than epoxy higher than the deck which won't stick to stainless steel, how about a thin layer of sikaflex 290/291 (can't remember which is which) this would allow for a tiny amount of movement. We actually used ordinary bathroom sealant on ours because I plan to do them every 2-3 years so want to be able to lift the chainplate deck cover.

I have a good friend who used to race the smaller 33 OODs, quite sucessfully too. He tells a good story of when new the way to tune the rig was tighen the back stay until the heads door jammed. Shave off 1/2" off the door and tighten the back stay again until the door stuck a second time, then it would be fine

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