Mold maneuvers

Sept/Oct 2002

Of particular interest to potential buyers of sizable voyaging yachts is a growing trend away from permanent female molds. For one-off and limited-production projects, it’s frequently more cost-effective to put extra effort into the fairing and sanding of large parts, as opposed building (and later storing) high-quality, female molds. One-off foam construction works well with inexpensive, frame-and-stringer molds which can be quickly and accurately constructed with the aid of CAD (computer-aided design) technology. One popular building method entails planking directly over temporary female mold frames using thick foam strips-an approach the eliminates even the mold stringers. Once the composite inner skin has been applied and the bulkheads, longitudinal framing etc. installed; the builder has a relatively rigid hull that’s ready to lift out of its temporary mold.

If a frame-and-stringer mold is used (either male or female), it’s often possible to apply wide vertical foam planks or even full-sized, heat-softened foam panels. This not only speeds construction, but reduces the “mileage” of bonded seams in the foam core, saving a surprising amount of weight. With any of these one-off building methods, the exterior fairing task that follows “de-molding” is relatively painless because foam sand easily. In relatively flat areas, a new generation of large-disc random orbital sanders can be often be used instead of traditional hand longboards.

After laminating the outer skin over the foam and final fairing, the preferred exterior finish is usually a two-part LPU paint. Modern paints are not only extremely durable and glossy, but weight much less than a gel-coat finish (which is typically 8-10 times thicker). On the average voyaging yacht, substituting paint for gel-coat will save several hundred pounds, and for multihulls with their much greater surface areas, the savings are even more impressive.


By Ocean Navigator