Leakage/Wet Core (image #3)
What: Water-soaked core between fiberglass skins
Where: Hull, deck, topsides — global
Why: Improper build or accessory installation
Fix: Costly rebuilding and recoring
This type of construction is common in light, fast boats. Core materials could be cork, balsa, PVC or urethane foam and various honeycomb materials.
I have seen water leak into cores for reasons including: bad isolation of the core at through-hull fittings and portlights; screws penetrating from the interior installation; and fasteners that are not properly sealed. Wet core can be detected using a $400 moisture meter, a small investment compared with the cost of your boat.
Wet core often reveals itself by inducing distortion. This can be seen in the flatness of the gelcoat finish and/or as a rippled appearance. Dark color can contribute to the distortion. A dark hull’s temperature may reach 210 degrees F in high summer. A white hull might hit only 160 F. Wet core is soft, and the heat makes it softer. The shrinkage stresses that naturally occur in the skin pull and push on the core and result in distortion. If you own a cored vessel, look for this type of change in the finish.
Discoloration coming from fittings is another sign that water absorption could occur. Wet core may also freeze, resulting in cracking caused by venting or expansion.
In the photo above (image #3), the laminate cracked along a hard spot created by a stiffener, but was exacerbated by the soft core, which is clearly indicated by the brown liquid in the crack.
All of these telltale signs in the finish could lead to expensive repair bills. Know what you are buying. Do a bit of digging into how the vessel is constructed. Many marine surveyors can find these problems, but sometimes they are very subtle and require an expert eye to spot. Samples can be taken and professionally analyzed. Moisture meters, ultrasound and core samples represent cheap insurance in making sure that your purchase will be a good one.