Cored decks or hulls or both

Published on December 11, 2006 by in Talk


Here are two pictures of what Mike and I are talking about when we say,”cored decks or hulls or both”

The first is a drawing of a cross section of cored fiberglass.  Fiberglass is laid-up in a mold then the coring material is laid over the fiberglassand another layer of fiberglass is layed over that sandwiching the core material in the middle.  The resulting composite is strong yet much lighter than solid fiberglass, as long as the structural integrity of the coring remains as is.

The second is a photo of a boat only a year old, that had an improperly bedded hatch and unsealed balsa core in the hatch opening.  Trim around the hatch opening has been removed to show the core and the rim of the hatch hides the top layer of fiberglass from view in this photo.  As you can see the balsa is already showing signs of deterioration.  If I hadn’t rebedded the hatch the core would be totally rotten in a few more years and the structural integrity in that area would have been shot.


Cored is good, unless it is bad. The most usual trouble, like our example here. is water getting into the deck followed by delamination and composting. Especially in the kinds of “affordable” yachts most are familliar with, the most important steps in building with cores are unseen, a pain in the ass for the builder, and usually let go in a job already with too much labor.

The right way to deal with a cored deck is everywhere the edge of the stuff is exposed it must be cut back and sealed. Companionways, hatches, dorade tubes , and hawse holes and so on. Everywhere deck fittings are attached the core should be replaced with solid blocking, and especially where things are under stress like winches and mooring cleats, chain plates, and so on. Ideally the core is back from the edge and sealed with epoxy,and then sealed in again with epoxy putty back out to the edge.

What can be done with a bad deck? Untill things get too far along you can attack the holes and edges, and of course always make sure everything is well bedded. When the deck is spongy everywhere and leaking below you may need a deck-ectomy. Simply (that’s a boat joke because it is all about details really) remove everything on deck, cut through the top skin all the way around as close to the edge as possible, peel the top of the deck off and carefully save, remove and replace the old core with something new and/or better, put the top of the deck back, reinstall everything right this time, and don’t forget to fix up the crack left by the cut. Maybe cover it with a nice wood deck that doesn’t even have to be too thick. M.J.

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