How much of my core is wet?

[dennisvetter]

I purchased a 1970 C&C 30' a couple of years ago. She's my first boat of this size so I'm pretty new to boat repair but love to tackle things myself. I love this boat and really want to gradually bring her back up to snuff. Before I invest too much in her I want to make sure I'm not "painting over rust" so to speak.

What I'd like to know is the extent of my core is wet as it will be a pivotal piece of information for me.

I have found some areas which were wet so I know I have some issues although I don't have any delaminated or spongy areas on the deck. The deck under the traveler was damaged as were a couple of areas around chainplates/stanchions (but not all). The chainplate/stanchion areas seem to be pretty isolated and I've successfully repaired them. The area under the traveler was fairly extensive (~2 sq. feet).

After I found the traveler problem I went "looking for trouble" last fall and borrowed a moisture meter from the yacht broker I purchased her through. I found a number of areas where the meter readings indicated it was wet. So I did an exploratory surgery (i.e. cut a 1" diameter hole into the core from the cabin in an inconspicuous place) and ... it was bone dry. (I'm hoping it's the case of a good tool in the hands of a bonehead ... ).

My questions are:

1) what's the best way to determine the extent of moisture damage ... unequivocally without too much exploratory surgery if possible. Are the moisture meters pretty reliable and "bullet proof" or does it take someone who really knows how to use it (and when they might be getting a false positive)?

2) if exploratory surgery is necessary, what's the best way to go about it without creating an ugly mess of my beautiful headliner (it's really pristine)?

Bottom line: any/all ideas about how to sort this out would be greatly appreciated.

Thanks in advance!!

[CrazyRu]

I used thin drill bit to puncture inner skin and get to wood. I found quite a few places where core was dump, and two areas where core was wet.
I don't have a headliner - easy job for me.

It seems like mousture meters are just another gadget without real use, they are not reliable...


Vlad
Freedom 28 Cat Ketch

[artbyjody]

You should invest in a real pro / surveyor for this. Seriously, drilling out a partial core from underside doesn't mean that your readings were wrong - but then again, without understanding how to use one, and the sample you took doesn't show - doesn't mean you did it right.. its really a catch-22.

This is one area you do want to BE RIGHT on - to begin with...if you talk to a surveyor and state all you want is a moisture analysis you can get a break off normal surveyor rates....

Be upfront - and they will work with you... otherwise - less you pulling out stantions with your bare hands, foot going through the deck, or spongy feels... you play a guessing game...a very expensive one at that...

[CrazyRu]

The only thing surveyor can say with some certainty is if there any delamination
That knowledge comes from sounding with a hummer as a primary tool. Rest of it is just a game of guesses. The sandwich may be strong and sound and has core saturated at the same time. Surveyor can say that there is some inconsistency in meter’s readings in some areas, however drilling holes is the only way to know what is exactly going on there…

[artbyjody]

Originally Posted by CrazyRu

The only thing surveyor can say with some certainty is if there any delamination
That knowledge comes from sounding with a hummer as a primary tool. Rest of it is just a game of guesses. The sandwich may be strong and sound and has core saturated at the same time. Surveyor can say that there is some inconsistency in meter’s readings in some areas, however drilling holes is the only way to know what is exactly going on there…

Not if you have a good surveyor.. CardiacPaul has posted several times (search moisture)...its a skill not a science.. maybe some science but lots more skill... drilling and tapping may work if you are looking for oil - and just like if you were - you'll usually end up disappointed and only introducing the next round of "thats where the water that caused the rot to begin with" game...becuase whatever you drill you have to seal and that is your next issue to worry about down the road...

A hammer sounding is NOT a primary tool...

[telekitr]

I have recently pulled up the teak deck on my boat with the plan to clean up the core (replace if necessary), fair over with a new top layer of fiberglass, awlgrip and non skid the deck. Teak is gone forever. I have borrowed a moisture meter. At first when very cold outside (boat in under a shed) the entire boat read wet??? Asking my fiberglass guy he told me that moisture meters are just another tool, sometimes not to be trusted. Air voids in the core laminate will come up reading wet!!! I have drilled similiar exploratory holes as you state. I come up with wetness around the screws that held the teak down and dry core in between the rows of screws.....which was a relief. Bottom line for me is that I will rely on drilling holes to get small core samples ( from the outside since I am going to refair and renonskid anyway and its much easier. I simple bore down through the top skin of fiberglass and into the core to inspect) being careful to keep the inner skin in tact.
Moisture meters might be fine for solid core hulls when one is trying to determine moisture as relates to blisters but core decks need to be backed up with exploration or one could go through an awful lot of work for nothing.

[paulk]

Moisture meters are notoriously fickle things. Sometimes they pick up moisture in voids (see above) other times they find moisture in bottom paint. Sometimes they may read wet because of the conductivity (copper bottom paint??) of the surface they're placed against. Core samplings are a good way to determine the actual "for real" situation, but they mean having to repair all the holes afterwards. We've done it with our boat, and found a large spot in the hull that needed work. I went at it from the inside so I wouldn't have to re-fair the hull, with supports holding the damaged area. Keep a fan going to get the fumes cleared!

[dennisvetter]

Thanks to all for your insights. It sounds like I need to do a little careful exploratory surgery. I think I'll use the moisture meter results to decide where to explore.

Again, I thank you all for taking the time to respond. What an incredible web site thanks to all of you!!

[cardiacpaul]

Dennis,

before you do a core-ectomy with a dremel, call a surveyor, tell him your problem... you'd be surprised, he might just know what he's doing and be able to lend a hand on the cheap (relative term).

I'd hate to see you drill and fill a stack full of holes when you don't need to, or miss spots that you really need to fix.

(hint), if the guy comes with ONLY a meter, send him packing. Same if he only comes with a "phenolic" hammer(I can charge more if I call it "phenolic" rather than a harbor freight 3 dollar plastic hammer)

I've used the handle end of a 12" hard yellow plastic screwdriver with the same results.

Theres one guy that I'm trying to learn from that uses a small paint roller, that seems to work as well, but haven't got the knack of that one yet.

Meters are a decent starting point, but they certainly aren't the do all, end all. Heres a little test for you.
take a reading where the meter says its wet.
Now, tap, tap tap.. remember that sound, drill your pilot hole, gander....

Is it?

If so, take another reading where the meter says its dry...repeat, is there a difference in the sound? if not, throw the damn meter away and hire someone.

This all can go kaflooey (thats a technical term we professionals use) if its rained a lot over the past week, if its been hot, if the boat has been in the sun, if your SO looks good in a thong, If your bananas haven't turned blue... point being, there are SO many other issues to take into consideration, a meter only just ain't gunna do the trick.