Moisture in cored hull

[PBzeer]

Looked at a boat this week that has a cored hull. It had been surveyed for moisture, and then surveyed again for insurance purposes, and was deemed acceptable. There were markings that ranged from 10 to 25 in the area that had been looked at. I'm wondering if anyone knows just "how acceptable" those kind of numbers are for moisture.

Thanks,
John

[administrator]

I can't answer your question directly, but take a look here. Very informative.

http://www.yachtsurvey.com/moisture_meters.htm

[captlar]

John - The numbers alone do not mean anything. Depends on the calibration and equipment. Few questions - What make of boat ? You said cored hull - you mean above waterline only or entire hull ? Did professional surveyor do the testing ? What was their opinion ? Was the boat "short hauled" or had it been on the hard for some time ?

Larry

[PBzeer]

Larry,

Boat is a Niagara 35 and has a completely cored hull. First survey was done by a regular surveyor, 2nd by someone specializing in hulls. Not sure how long boat had been on the hard prior to survey, but it is still on the hard. Beyond that, Both surveyors claimed the numbers weren't that high for a 20+ yr old boat. Beyond that, I have no info

John

[captlar]

John, cored below the waterline is scary for some, including me. Coring waterline up is common for lateral stiffness. If you are (or can get) comfortable with all core hull, and the readings are consistent over the entire hull, rather than specific areas of concern, you may be fine. I assume there were no problems at thruhulls and other penetrations. If the boat will have seasonal use so it can dry out during the offseason, better still. Higher moisture readings are common in core decks on older boats, and sounding is (I believe) the best way to determine if you have trouble. Supposedly, balsa core material was used on Niagra and they are supposed to be good sailors and well built. I would call a few more surveyors and/or brokers to get their opinion on Niagra and specific issues. Practical Sailor will sell you a report on the boat, but you never really know what you are buying.

Larry

[paulk]

Everything is relative, and moisture readings are tricky. Prior to purchase, our new (to us) J/boat showed "very" wet core, all over the place. The surveyor said - "walk away". It had been a REALLY cold winter with lots of sub-freezing weeks, though. We reasoned that if the boat was as wet as he claimed, the freezing should cause delamination. He could'nt find any delamination. A second surveyor (second opinions can be very valuable) ran his moisture meter over the outside of the hull and found high moisture readings, as did the first. From the inside, however, putting the meter against fiberglass that hadn't been painted, the readings showed mostly dry. The paint (tired awlgrip on the topsides, and an ablative on the bottom) was apparently retaining moisture and the meter was showing this. We bought the boat and kept our eye out for delamination problems.

About six years later, when we had her topsides repainted, the yard reported finding some hollow-sounding spots below the waterline. We had them drill out some sample plugs (four) to see what was happening. One was wet - water could be squeezed from the balsa, and it was no longer bonded to the outer fiberglass skin. The other three were ok- they simply sounded hollow when tapped. We sailed on it for another season before deciding it really had to be fixed.

Rather than go nuts with re-fairing the outside of the hull after a repair, we decided to make the repair from the inside. There's also something to be said for applying resin so it flows down into where you want it to go, rather than trying to get it to flow up overhead and having it drip down on you instead. I started by shoring up the outside of the hull with stringers to hold the hull shape. Then I found the spot (inside) where the test boring was, and used a dremel tool to cut through the inner layer of fiberglass. I enlarged the cut as I found wet or delaminated balsa until it was a rough oval about 24" x 30". The problem had been caused by screw used to secure the engine control cables with a cable tie as they went from the pedestal to the engine. A workman had screwed it into the inner layer of the hull instead of to part of the after bunk framing. Drops of spray or condensation slid slowly down the cables for about 20 years and were directed into the core by the screw. After opening it all up to "solid" material, I let it dry out some more for good measure for a week or so, with a lamp helping. Then I filled in new balsa core, used resin to stick it to the outer hull and 'glassed it over again on the inside. Soup to nuts, it took about three Saturdays (and not all day, either.) Paying someone to fix this would probably have cost about $3,000.

So...moisture is something you have to expect on a boat. How you deal with it depends on the severity of the problem, how extensive it is, and where it is. Maybe it's extensive enough that you don't want that boat. Maybe it's not so severe that you can't live with it. Maybe where it is means you can offer a lot less and still get a nice boat. Everything on a boat is a balancing act - what you like, don't like, want, don't want, need, don't need, and how much you're willing to pay and how much the seller's willing to take. Find out as much as you can (as you are) and good luck.

[captlar]

paulk - Interesting read. Amazing how one guy with one screw can create such a problem. I won't sleep well tonight. I am curious. When describing coring three of the possible problem areas you said you found no problem and "they simply sounded hollow when tapped". Does that mean you did a sample core and did not find a void in the layup, but simply had an "innocent" sounding caused by thinner hull or other unknown ?

Larry

[sailingfool]

John,

If you read Mr. pascoe's article about cored hulls, http://www.yachtsurvey.com/cored_hull_bottoms.htm, it may resollve the question for you completely. My personal opinion - there are plenty of boats with solid glass hulls, why look for extra problems? PAULK would probalby the risk he took turned out OK, but who needs it? As unlucky as he may have been, in context of the the risk, he was very, very fortunate.

[paulk]

Originally Posted by captlar

paulk - Interesting read. Amazing how one guy with one screw can create such a problem. I won't sleep well tonight. I am curious. When describing coring three of the possible problem areas you said you found no problem and "they simply sounded hollow when tapped". Does that mean you did a sample core and did not find a void in the layup, but simply had an "innocent" sounding caused by thinner hull or other unknown ?

Larry

It did take about twenty years for the problem to need fixing. On the hull sounding -- interior structures - floors, ribs, bulkheads, engine mounts, tanks, cabinets, furniture, etc. can all create little pockets in a hull that sound "funny" when tapped. This is without mentioning starved laminates, voids, and actual delaminations. The borings all showed the same hull thickness (and laminate schedule), but we'll still keep an eye (and an ear) out for anything that changes. It's a boat. You never know.

[captlar]

Thanks Paul - Interesting ! Larry