Absolutely nothing does more damage to more boats than water penetrating the deck core. Not hurricanes. Not inadequate
ground tackle. Not electrolysis. Not leaking propane. Not anything.
It shouldn’t be that way. On any well-constructed boat, core damage is entirely preventable. That it continues to occur, continues to be epidemic, suggests that many boat owners still fail to make the connection between cause and effect—until it is too late.
Conventional fiberglass is inherently flexible, so boat builders stiffen the deck by sandwiching a relatively thick core between two thin fiberglass skins. The core is sometimes foam, sometimes plastic honeycomb, but most often wood. This I-beam-like technique yields a deck that is strong, stiff, and light. And vulnerable.
When the deck pops out of the mold, the core is entirely encapsulated, presumably good for the life of the boat. But then someone comes along with a drill or a saw and opens the skins. Water gets to the core through these openings. This bears repeating. Deck core damage is invariably the direct consequence of drilled or cut openings in the deck.
Some enlightened manufacturers make accommodations for this truth by replacing the core with solid lay-up where openings will be cut or factory hardware will be attached. More often plywood is substituted for foam or balsa in the hardware attachment areas. Plywood provides much higher resistance to compression, but from the standpoint of susceptibility to water damage, it is hard to imagine a less suitable material. Water wicks through plywood like milk through Shredded Wheat.
In any case, factory hardware is just the beginning of the problem. Virtually all boats have a myriad of things attached to their decks by their owners, and every hole drilled into the deck adds to the certainty that water is going to find its way into the core. When it does, the core begins to deteriorate, either due to rot or to saturation. Eventually the bond between the skins and the core releases, and when this happens, the paradigm that describes the deck changes from I-beam to leaf spring.
Repairing even a small area of core damage is a big job. The cost to repair a completely saturated deck can easily exceed the value of the boat. So the best plan is to be vigilant about maintaining core encapsulation. That doesn’t mean you have to bond your hardware to the deck (although for some items, this certainly has merit) but it does mean that the process for installing deck hardware is more exacting than just putting a bead of sealant around the fasteners. All that is required to maintain the integrity of the core is to reseal with epoxy resin the edge exposed by cutting or drilling. This adds a step or two to every deck hardware installation, but the additional effort pales compared to even the smallest core repair.
Here, then, is how to install deck hardware without opening the door to water damage to the core.
Cut openings If you are installing a
hatch, a portlight, a vent, a chain pipe, or any other item that necessitates cutting a hole in the deck, you will have exposed core all around the perimeter of the hole. Depending on a bead of sealant between the hardware item and the deck to keep water from reaching the core is a sucker bet. The question is not if the sealant will leak, but when. And when it does begin to leak, you won’t know about it because the core will be sponging up the trickle.
Simply painting a coating of
epoxy onto the edge of the core is similarly imprudent. You want more than a paper-thin membrane keeping water out of the core. To make space for a more substantial barrier, chisel or grind the core material back from the edge of the cut opening approximately ¼ inch. A Dremel-style rotary tool can make short work of preparing the desired recess.
Mix a few ounces of epoxy and thicken it with colloidal silica to a consistency stiff enough not to sag. Trowel this mixture into the recess, filling it flush with the edges of the upper and lower skin. When the epoxy has cured, you may need to clean up the edge by sanding. After that, the cut opening is ready for whatever will fill it. You still need to set the hardware item on a bedding of sealant, but now when the sealant eventually loses its grip, the consequence will be a drip on your head, not damage to the core.
Drilled openings
For protecting the core exposed by drilling holes in the deck, the idea is the same but the technique is somewhat different. Start by drilling the hole two drill sizes larger than the fastener requires. Next, you want to recess the core around the hole in a manner similar to what I just described for a cutout, but this is made somewhat more difficult by lack of access. The answer is a bent nail. Hammer a nail over a metal corner into a 90 degree bend, then cut of the head to leave a straight shank, and cut off the bent end as close as possible to the bend. When chucked in a drill and inserted into the drilled hole, the cut-off end will gouge out the core material as you run the spinning nail around the edge of the hole. Blow or vacuum out the pulverized core.
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Mix up a small amount of epoxy and thicken it to ketchup consistency with colloidal silica. Tape the bottom of the hole closed, then pour or better yet inject with an epoxy syringe the thickened epoxy into the hole. You want to fill the hole level full, taking care to avoid leaving any air in the fill. If you don’t have a syringe, use a piece of wire to agitate the epoxy to release any air.
That is it. Once the epoxy has fully cured, redrill the hole, this time to the correct size, and install the hardware the way you would have before, seating it on a sealant bed.
For small holes for small items screwed rather than through-bolted to the deck—twist fasteners for a dodger, for example—digging out the core becomes impractical. But you cannot ignore these holes or they will surely let water into the core. The technique that I use is to drill through the skin, then ream out the core in a somewhat larger circle by moving the drill off the vertical and rotating it at that angle all the way around the hole. The result is a cone-shaped hole with the apex at the hole in the deck and the base in the core. The drill brings out the removed core material. When you fill this cavity with epoxy, then redrill it, your screw is attached to the deck skin and the part that would otherwise extend into the core is now inside this protective cone of resin.
Be vigilant about keeping the core fully and completely encapsulated and you will avoid the considerable unpleasantness of saturated core.
