Moisture measurements in sandwich hull

[Captain Krook]

Hi everybody! We are considering buying a Contest yacht from the nineties. The hull is a sandwich construction with balsa as distance material.

After it dried out on the ground for two sunny days a professional surveyor measured the moisture levels in the hull. He found high levels (70-100) in two areas, one maybe half a square meter, the other maybe a little more than a square meter. The hammering sound test indicated no problems with the structure (good strong sound). The boat is generally in good condition, and appears to have been well taken care of.

The broker says that there is nothing to worry about, and that the surveyor should have emptied all tanks, pipes and hoses before surveying. I know that moisture measuring is tricky and often gives false answers.

– Should we walk away?
– If the worst would happen – rotten balsa – will it cost like 10.000 dollars or more like 100.000 dollars to have it professionally fixed?

Happy for any thoughts on this!

[SailFastTri]

There are so many variables possible that nobody here can give you a reliable answer, based on the information you posted. The following link is a good read if you want to learn more:
Moisture Meter Mythology and Flir thermal imager

As for repair estimates, you would need to get someone who can do the repair to give a first hand assessment and estimate. Anything else is speculation.

[rognvald]

Captain,
The Contest is a great boat. Although it is possible that there is a core issue, I would not take the word of a surveyor as gospel. Surveyors are like baseball players: some hit 350; others hit 220. And, sadly, some do not belong in the Big Leagues. If I liked the boat, I would agree on a price contingent upon a core sample taken in the problem areas by a marine fiberglass specialist who repairs boats for a living. If it is wet and repairable, make the repair a contingency before closing. If he finds it was a mistake by the surveyor, make your best deal and buy the boat. I have no axe to grind with professional surveyors and I'm certain there are some excellent ones across the country. However, if you have a plumbing issue with your house, don't call the contractor . . . get the plumber. Good luck and safe sailing.

[Cyrus Safdari]

There's always some moisture in a balsa core. Dealing with that is not the big deal but finding the cause is really more important because that could indicate a far larger problem than just moisture in the hull. So the real question is WHY there's moisture there.

Moisture in the core around fittings, penetrations and places where the boat took a bump is pretty normal and a logical place for moisture to be. It isn't great but "to be expected". It is just a result of a badly done job when the fitting was installed, or over time the caulking around the fitting has given up, or a crack in the fiberglass has allowed water intrusion. This is why some people avoid boats with balsa core hulls

Moisture in places on the hull that are not close to fittings and penetrations can be a bigger deal. For example, apart from pox, if the high moisture levels on the hull is behind where the ice box is located, could mean that water has found its way into the insulation *from inside the icebox* and so you'll need to tear out the whole thing and redo it.


The bottom line is that eventually moisture will cause delamination if it is not stopped. It is only a matter of time, like a bad tooth. Maybe a long time. Maybe not.

Fixing rot in core is really not that big of a deal: cut the fiberglass, dig out the core and grind around the hole, stick in some foam and filler, glass over it. Can be done by non-experts. Plenty of Youtube videos. The real pain is then trying to make the patch match the rest of the boat. This may require repainting the whole thing. Which means stripping off the old paint, filling and fairing, sanding some more, priming, at two coats of paint expertly applied so as to not show brush strokes etc etc. A big job. Of course under the waterline any patch would be covered by antifouling.

Whether you should walk away or not is a personal question and depends on your finances, willingness to DIY, cost of labor around you etc. There are always other boats! BUT any old boat will need work. That's just life. Some of us like it! It is just a question of first figuring out what the problem *really* is before buying in.

[Cheechako]

"– Should we walk away?
– If the worst would happen – rotten balsa – will it cost like 10.000 dollars or more like 100.000 dollars to have it professionally fixed?"


I would pass on fixing with a couple caveats. It can balloon into a lot. For one thing, you are going to need at least one side of the hull painted after repair. More likely you will want to do both. Painting alone will eat up the $10k.
Questions:
-are the "wet" areas accessible from the inside? You can cut and replace core from there with a lot less cost.
-would the owner let you drill a few small holes on the inside to confirm or deny wet core? If you drill into the core (not thru!) the areas that show as "wet" with a 3/16 drill, then take the core material off the drill twists and squeeze it between your thumb and forefinger. If very wet.... water will come out. You can also see if the inside fiberglass is tight bonded to the core also.
-Some boats have nearly a fully thick hull outside the core, in this case I think it matters less if there are a couple of smaller areas of wet or unbounded. But with modern light boats, the outer hull may be very thin.
-Is the hull fully cored? Can you see if the core was eliminated around the seacocks? (it should be evident if it was)
-How far from the keel does the core stop? (it should be evident where it stops)