PS Advisor January 1, 2000 Issue

PS Advisor

Cored Hull Concern
I write in hopes that you will be able to tackle a fundamental question. Our family, which has been involved one way or another with sailboats since the 1930s, finds itself boatless and in the market. Like most sailors, we are conservative about our sport, preferring a proven design or construction method over the latest innovation. I remember well my grandfather’s misgivings over whether fiberglass was a suitable material with which to build a boat. I have sailed since boyhood on older boats; the last boat in the family was built in 1972.

Of course, there has been no real need to own a newer boat. Solid fiberglass boats are still going strong. Early fiberglass boats such as the Bounty II and the Triton are 40 years old—still sailing when boats made of wood, the material fiberglass replaced, would be at or past their expected useful life. But, and here is the question, what of the cored fiberglass hull, the material that in many high-end boats replaced the solid fiberglass hull? Some of the cored boats are approaching or past 20 years old. Has the time come when one can say whether the cored hull will exhibit the same amazing durability of its solid ancestor? If so, what do you think?

Certain potential problems are obvious. Plainly, there is a potential for delamination, at least in comparison with solid hulls where there are no laminations to come unstuck. Water can enter the core if there is a breach of the outer skin, with results that would surely be undesirable. It now seems true that all fiberglass hulls will blister to some extent, given enough time and immersion m water. This may or may not be a particular problem for cored hulls.

The point is, will these problems inevitably crop up, and make the life expectancy of a cored hull finite compared to a solid hull? Some respectable and conservative boat builders build very expensive yachts with cored hulls. Sabre for one. Alden for another. I read that even Migrator uses an Airex core for the classic Block Island 40. On the other hand, boats are still being made with solid hulls. Practical Sailor has reported that Tom Morris of Morris Yachts prefers not to build a cored hull. The performance benefits of a cored hull are self-evident. Can it be that builders of high-end cored boats are aiming at a sector of the market that will simply replace an older boat?

I doubt that we will ever run with the disposable boat crowd. We, and many like us, have been coaxing yet another season out of old boats until it has become a part of the lifestyle. But, absent an accident or neglect, can we expect that cored hulls will be around and keeping their value after 30 years, or 40? When the supply of affordable older boats is dominated by cored hulls, what do you recommend?

E. Evans Wohlforth
West Orange, New Jersey

A variety of cores are used in modern boats, primarily end-grain balsa and foam, such as Airex and Divinycell, among many. Our 1975 Tartan 44 is cored with Airex and shows no signs of delamination or degradation.

Your concerns, however, are not without foundation. The potential for problems with cored construction do exist and usually can be traced to the builder’s workmanship and/or abuse by the owner.

Cores make for stiffer, lighter panels than any reasonable thickness of solid fiberglass. Quality is improving constantly and more builders are learning how to work with them. Still, everyone has an off day or a learning curve when switching to a new process. In terms of workmanship, voids between blocks of core should be filled with resin but often are not. The edges of coring should be feathered where the core terminates at the deck or anywhere else, such as on hulls that are cored just above the waterline. Coring should be removed around through-hulls; you can usually see a depression around the through-hull indicating this.

We do have to disagree with your statement that “all fiberglass boats” will eventually blister. This doesn’t appear to be true, though blisters remain a concern. Marine surveyor Jonathan Klopman told us that erratic moisture meter readings on the bottom of a cored hull suggests cutting a plug for lab testing. Erratic readings on the bottom of a solid skin hull is not so much a worry, he said.

Delamination is probably a bigger worry. The causes run from poor bonding of the skins (possibly due to the builder waiting too long after lay-up of the skin before adding core, or using too little resin) to collision in which the trauma cracks the bond between skin and core. Fractures can run a considerable distance from the point of impact. Cored hulls are invariably more expensive to repair.

Properly built, operated and maintained, a cored hull should last as long as a solid one. Simply because a cored hull is more intricate, however, there does exist a greater possibility of trouble.

In the end, the best advice is to hire a good surveyor, whether buying a used or new boat.

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