![]() ![]() In such instances, woven roving is in fact weaker than chopped-strand mat. Any woven fabric with fibers oriented at 0 and 90 degrees is weakest when resisting loads imposed at a 45 degree angle. If the load path, however, runs at an angle to the fibers, their strength decreases proportionally. Though the fibers are crimped by the weave of the cloth and so lose some unidirectional strength, they are long and continuous and thus much stronger than the short fibers found in chopped-strand mat if they are oriented in more-or-less the same direction as the load being imposed on them. Here bundles of fiber-those rovings just mentioned above-are woven together at right angles into a loose, bulky cloth. The next coarsest type of fabric is woven roving. However, because they are thick and contain a lot of resin, they are quite heavy and have poor strength-to-weight ratios. Such hulls are perfectly sound if built thick enough to compensate for the short fibers they contain. In the early days it was common to see entire boats built of mat, and after the advent of the chopper gun in the mid-1960s it became even easier to build hulls of nothing but chopped fiber. ![]() Though messy to work with, chopper guns make it easy to build up laminate quickly. Pull a trigger and a gooey mass of catalyzed resin mixed with chopped fiber spews forth from the gun. This device cuts continuous bundles of fiber called rovings into short strands and spits them out into the air while simultaneously expectorating streams of resin and catalyst. Because the fibers in mat are randomly oriented it is equally strong in all directions, but because the fibers are also very short, it is not as strong as fabrics with longer continuous fibers.Ĭhopped fiber can also be laid down in (or on) a mold with a chopper gun. Because it becomes quite malleable after its binding agent dissolves, mat is particularly good for working into crevices and corners in a mold. Mat also bonds well with other layers in a laminate, particularly other layers of mat that are still wet with resin, as the fibers from each layer can then intermesh with each other. This makes it possible to build up thickness in a laminate with minimal effort. Mat is easy to work with because it wets out quickly and is bulky. The fibers are held together by a light binding adhesive, usually a polyester powder or polyvinyl acetate emulsion, that dissolves when exposed to resin. The crudest fabric is chopped-strand mat, or mat, which consists of fibers chopped into strands up to 2 inches long that are laid down in a random pattern and pressed into a spongy, felt-like material. Various types of fabric have different properties and different types are usually used together in the same laminate. Still, early solid hulls were built very robustly and many show little sign of deterioration even 40 or 50 years after they were first created.Īs I mentioned last time, the major ingredients in any solid laminate are resin and fiberglass fabric. This is not true, and you’ll often find solid laminates in older boats are a bit thinner than their owners like to believe. There is a popular myth that early glass hulls were built as thick as wood hulls because builders didn’t know how strong glass was and wanted to play it safe. Solid hulls were the rule in the early days of fiberglass boatbuilding and many are still found in both older boats and new boats. To understand fiberglass lamination, it is best to focus first on simple solid laminates in which multiple layers of fiberglass fabric are built up to the thickness necessary to make a part strong enough to do its job. ![]() Now we need to talk about the business of building up a glass laminate within a mold in more detail. In my last missive on this subject I introduced the concept of building fiberglass boats in female molds, just like the one pictured here. ![]()
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