A Guide to Composite Materials in Boats

A Guide to Composite Materials in Boats Composite materials are broadly defined as those in which a binder is reinforced with a strengthening material. In modern terms, the binder is usually a resin, and the reinforcing material consists of glass strands (fiberglass), carbon fibers or aramid fibers. However, there are other composites too, such as ferrocement and wood resins, which are still used in boatbuilding. Composites offer the advantages of a higher strength-to-weight ratio than traditional wood or steel methods, and they require lower skill levels to produce an acceptable hull finish on a semi-industrial scale. History of Composites in Boats Ferrocement Probably the earliest use of composites for boats was ferrocement. This material was extensively used in the first half of the twentieth century for building low-cost, low-tech barges. Later in the century, it became popular not only for one-off home projects but also for production boatbuilders. A steel frame made of reinforcing rod (known as an armature) forms the hull shape and is covered with chicken wire. It is then plastered with cement and cured. Although a cheap and simple composite, armature corrosion is a common problem in the chemically aggressive marine environment. There are still many thousands of ferro boats in use today, however – the material has enabled many people to realize their dreams. GRP During the Second World War, just after polyester resins were developed, glass fibers became available following the accidental discovery of a production process using blown air on a stream of molten glass. Soon, glass-reinforced plastic became mainstream and GRP boats started to become available in the early 1950s. Wood/Adhesive Composites Wartime pressures also led to the development of cold-molded and hot-molded boatbuilding techniques. These approaches entailed laying thin veneers of wood over a frame and saturating each layer with a glue. High-performance urea-based adhesives developed for aircraft manufacturers were widely used for the new technique of molding boat hulls – typically for PT boats. Some adhesives required baking in an oven to cure and hot-molded hulls were developed, though there were size limitations governed by access to industrial ovens. Modern Composites in Boats Since the 1950s, polyester and vinylester resins have improved steadily and GRP has become the most prevalent composite used in boatbuilding. It is used in shipbuilding too, typically for minesweepers that need non-magnetic hulls. Osmotic problems from which early-generation boats suffered are now a thing of the past with modern epoxy compounds. In the 21st century, volume GRP boat production follows a full industrial production process. Wood/epoxy molding techniques are still in use today, typically for rowing skiffs. Other wood/adhesive composites have evolved since the introduction of high-performance epoxy resins. Strip planking  is one such popular technique for home boat construction: Strips of wood (typically cedar) are laid longitudinally over frames and coated with epoxy. This simple construction offers a cheap and strong build with a fair finish easily achievable by an amateur. At the leading edge of boat building, aramid fiber reinforcing strengthens key areas of sailboats, such as the bows and keel sections. Aramid fiber also provides improved shock absorption. Carbon fiber masts are increasingly common, as they offer major performance and vessel-stability benefits. Sailboats also use composites in their sail construction, with carbon-fiber or glass-fiber tape offering a flexible but dimensionally stable matrix to which synthetic sailcloth is laminated. Carbon fiber has other marine uses too – for example for high-strength interior moldings and furniture on super-yachts. The Future of Composites in Boatbuilding The costs of carbon fiber fall as production volumes increase  so the availability of sheet carbon fiber (and other profiles) is likely to become more prevalent in boat  production. Materials science and composite technology are advancing rapidly, and new composites include carbon nanotube and epoxy mixtures. Recently, a small naval vessel with a hull built using carbon nanotubes was delivered as a concept project. Lightness, strength, durability, and ease of production mean that composites will play an increasing part in boat construction. Despite all the new composites, Fiber-reinforced polymer composites are here to stay for very many years, though it will surely be in partnership with other exotic composites.