Core construction is not without its problems, though. Anything that disrupts the bond between the fiberglass skins and the core will result in a weak and "spongy" deck, which gives under your weight. While a bond failure can result from a shock load breaking the bonds between the skins and the core, a far more common cause is water in the core. In extreme examples, wooden cores can soften and rot. The resulting damage lowers the value of the boat, can pose significant safety issues and can be very expensive to repair.

Why all this emphasis on core problems? Because most of those problems are the result of improperly installed deck hardware. Mounting holes are often drilled through the cored deck and sealed only with some type of sealant. That works until the sealant fails and water starts leaking into the core. Often those leaks only show up below after core damage has occurred. Do not assume no leaks below means no problems with the deck.

PROPER LOCATION

Graphic by Paul Esterle The first step in installing a cleat is to find a location. Use some double-sided tape and mount the cleat temporarily. Try leading your dock lines to the cleat. Is there a wide range of angles for the line to access the cleat? Does the line contact any area of the hull that will chafe either the line or the hull? In some cases, you may need to install a chock to guide the dock line past obstructions and prevent chafing. Finally, you will need sufficient access to the underside of the mounting area in order to mount the cleat properly.

That last one is a biggy. A proper cleat installation, one that will stand up to both the stresses from the dock lines or a towing situation, must be mounted with a backing plate underneath. That plate distributes the forces applied to the cleat over a larger area. Cleats with no backing plates or only washers can pull right through the deck.

Once the proper location is found, it's time to drill the mounting holes. Do not even think about using self tapping screws or wood screws. Properly installed cleats must be through bolted. After you drill the fastener holes, it will be time to deal with that cored deck.

Deck crush is another potential problem. Tightening a fastener can crush the core under the fastener. To prevent both the leak and crush problems, we remove the core from around the fastener hole and replace it with epoxy mixed with high-density filler. In my case, I use W.E.S.T. Systems 105 resin, 206 Slow Hardener and 404 High Density Filler, but you should research what is best for your boat and your application.

Graphic by Paul Esterle Graphic by Paul Esterle There are several ways of removing the core from around the hole. You can make a tool from an Allen key by sharpening the end and chucking it in a drill (see illustration). You then insert the Allen key in the fastener hole and drill away, periodically vacuuming out the debris from the hole (see illustration). This technique works fine with a honeycomb or foam core, and adequately with a balsa core.

For plywood-cored decks, I use another trick. Select a hole saw slightly smaller than the base of the piece of hardware being mounted. Then use that hole saw to drill a hole through the top skin and the plywood core, but leave the bottom skin intact (see illustration). The center pops out with the twist of a screwdriver and you can clean out any remaining wood core from the bottom of the hole.

Once the core is gone it's time for epoxy. First, though, tape off the bottom of the hole completely. Failure to do this simple step properly will result in epoxy icicles hanging down from the underside of the deck. Paint the inside of the cavity with epoxy. This epoxy will prime the dry wood inside the cavity and prevent the wood from sucking the epoxy out of the epoxy/filler mixture. Once the inside is primed, mix high density filler and some colloidal silica like W.E.S.T. 406, which acts as a thickening agent, with the epoxy and fill the cavity (see illustration). Do it slowly to ensure no air bubbles get trapped in the epoxy.

After the epoxy has cured, the fastener holes are re-drilled. This time, however, you are drilling through a solid epoxy plug. Even if the sealant fails and the fastener starts to leak, that water won't end up in the core damaging it. The solid epoxy plug will also prevent you from crushing the core from over-tightening a fastener.

BACKING PLATE

If you haven't already done so, now is the time to make that backing plate. Backing plates are most often made from marine plywood, aluminum or stainless steel. Wood is the easiest to make, usually from ¾-inch marine plywood. The plywood must be completely sealed with several coats of epoxy before installing it, in order to prevent water from weakening the wood.