Harold Simpson of Dallas, Texas, asks:
"I was replacing the solar fan mounted in the front hatch of my 1987 Hunter 23, and when I removed the hinge screws, I found clear water in the screw holes in the cabintop. I also recently developed a leak in the cabin roof, which appears to be coming through the mounting screws of a block on the port side of the mast. The water is clear, so perhaps there is no damage to cabin core. How long will the water stay in the core? Should I seal every hardware-mounting hole and hope the water migrates out? Can I inject alcohol into the core to drive the moisture out?"
Don Casey replies:
Neglect is the number one cause of devaluation of older boats. Core damage is number two. If you are lucky, Hunter built the deck to accommodate the forward hatch hinges by making it solid in this area. Not all builders have been conscientious about this, so you need to probe the inside of the fastener holes with a sharp, stiff wire. The area around the mast should also be solid laminate, but probe these holes as well. If the sides of all of the holes are hard rather than soft or hollow, sponge the water out with rolled-up tissue. Then dry the holes out with a hair dryer and carefully re-bed the fasteners when you reattach the hinges. However, if your wire encounters any core or voids in any of the holes, you must take some corrective measures.
If there is moisture just around the hole, pouring in alcohol can help displace some of if, but if moisture has migrated away from the holes, it is trapped in there and cannot escape, particularly if you seal it in by reinstalling the screws. This would be like leaving a wet sponge inside a closed container.
To dry the core you must expose it to air. Leaving the hole open and protected from rain for a time may allow a modest amount of moisture to evaporate. If large areas of the core are saturated, it must be exposed, either by drilling a series of venting holes in the affected area or by removing all the top skin of the laminate. Tenting the boat with a dehumidifier inside the tent will accelerate the process.
To maintain the integrity of the deck, deteriorated core should be replaced. However, if your only clue is the trickle in the cabin, do not assume the worst. Lightly tap the deck around the holes with the round end of a plastic screwdriver handle. A sharp report indicates sound laminate; a dull thud indicates saturation and/or delamination. A small suspect area can be safely ignored if you take steps to prevent more water from entering. Treating small areas with penetrating epoxy is another option.
When fastening trim or hardware to a cored deck, the proper procedure is to drill each fastener hole oversize, then gouge out the core around the hole with a bent nail chucked into your drill. Vacuum out the pulverized core material. Screw holes should pierce the top skin and core, but not the bottom skin. For through-bolts—the only seaworthy fasteners for deck hardware—the hole through the bottom skin should be taped closed so you can fill the cavity you have created with epoxy that has been slightly thickened with colloidal silica. When the epoxy cures, re-drill the holes, which are now permanently separated from the core by the epoxy. Bed the fasteners properly when installing the hardware.