When it comes to boats, the leather and wood construction which St. Brendan used to cross the Atlantic does not qualify as the leather was stretched over a wooden framework – it doesn’t fit the modern, accepted definition of composites.
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 is glass strands (fiberglass), carbon fibers or aramid fibers. However, there are other composites too, such as ferrocement and wood/resin which are still in use in boatbuilding.
Composites offer the advantages of a higher strength to weight ratio than traditional wood or steel methods, and requires lower skill levels to produce an acceptable hull finish on a semi-industrial scale.
History of Composites in Boats
Probably the earliest use of composites for boats was ferrocement. This 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) is used to form the hull shape and 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 – the material has enabled many people to realize their dreams.
During the Second World War, just after polyester resins were first developed, glass fibres became available following the accidental discovery of a production process using blown air on a stream of molten glass. Soon, glass reinforced plastic (‘GRP’) came into use and GRP boats started to become available in the early 1950’s.
Wartime pressures also led to the development of ‘cold molded’ and ‘hot molded’ boatbuilding techniques. These were based on laying thin veneers of wood over a frame and saturating each layer with a glue. High performance urea-based adhesives had been developed for aircraft manufacture and were widely used for the new technique, 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 obvious size limitations.
Modern Composites in Boats
Since the 1950’s, resins (‘polyester’ and ‘vinylester’) have improved steadily and GRP has become without doubt the most prevalent composite used in boatbuilding. It is used in shipbuilding too, typically for minesweepers which need non-magnetic hulls. Osmotic problems from which earlier generations suffered are now a thing of the past with modern epoxy compounds. In the 21st century, volume GRP boat production follows a full Henry Ford-like 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 offer a cheap and strong build with a fair finish easily achievable by an amateur.
At the leading edge of boatbuilding, we are now seeing aramid fiber reinforcing being used to strengthen 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 being used as 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 are reducing continuously as production volumes increase (doubling every five years), and the availability of sheet carbon fibre (and other profiles) is likely to increase its use in production boat building.
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, FRP Composites is here to stay for very many years though it will surely be in partnership with other exotic composites.