Watching for Troublesome Deck Cracks

There are several things going on in this picture, all stemming from the small hairline cracks radiating out from where the chainplate pierces the deck. At first glance, they may not appear to be that serious. However, they will allow water to penetrate the outer skin and enter the balsa core of this high-end daysailer, setting off a series of problems.

In Northern states, at least, this water will freeze in the winter months. As it does so it will expand, forcing the crack to get a little wider and increase its length by an imperceptible amount each time, thus allowing more water in when the temperature rises again. The boat will go through many of these freeze/thaw cycles during a typical winter, and before you know it you have a real problem and a hefty repair bill.

Damage to the fiberglass may be bad enough, but the real danger is to the chainplates themselves. Crevice corrosion, the nemesis of stainless steel that is deprived of oxygen, could be eating away at the chainplate where it is hidden within the deck’s structure.
In this particular case I recommended that the cracks be ground out before filling and fairing with epoxy. The deck could then be repainted to match the original. I also suggested that the chainplate deck cover (the one with the fours screws) be lifted and the bedding caulk underneath be raked out and replaced to prevent water from getting into the deck by this route too. Not a huge job at this stage, but if neglected the damage could become extensive and the repairs far more costly.