Fibre Reinforced Plastics

Fibre Reinforced Plastic or FRP is a composite material consisting of reinforcing fibres thermosetting resins. Other materials such as fillers and pigments may also be present. Glass fibre is generally used as a reinforcing material, and polyester resins are usually used as a bending agent. The primary application of FRP is consumer products such as chairs trays, helmets, pipe ducts, water cooler bodies, water tanks panelling etc.

Equipment and Materials

The fundamental tool for the production of FRP vessels is mould. The most common type is the female mould which can be described as a reverse or mirror image of the finished hull, which allows the FRP materials to be laid upon the inside. It too is made of FRP and is cast from a “plug”, which is a reproduction of the hull or deck, faithful in size, shape and every detail.

The plug is the beginning of the process and is an exact hand-crafted replica of the final hull. It usually is made from wood and used only for casting the mould, and is then discarded. It requires high skill levels to achieve fairness and a smooth finish. But this is reproduced faithfully every time a hull is made, so the better the mould, the better the hull. It can be said that the first hull made from a new mould has been built three times:

WOODEN PLUG → FRP MOULD → FRP HULL

This gives some idea of the costs and effort needed in setting up FRP production. Therefore, it is essential to choose the most suitable design and produce at least a minimum number of boats to recover the investment made to produce the plug and mould.

For larger vessels, the tooling-up phase (plug and mould building) is repeated for the deck, wheelhouse and interior moulds, further increasing investment costs before a single vessel is produced. The sequencing of these tasks is complicated, and it is emphasized that thorough planning and careful choice of the vessel must be undertaken before commitments are made.

The main material components previously mentioned are reinforcement and resin. The most popular reinforcement used is a form of glass. It is processed into filaments, then woven or chopped and supplied in rolls similar to bolts of cloth. The thickness of the cloth varying with the weight of the glass in grams per square metre. The two main types are “chopped strand mat” and “woven roving”. In addition, there are two main types of resin at a functional level: “laminating” and “gel coat”. The former is a translucent liquid of various pale colours with a strong smell of styrene, which is characteristic of resins. The latter is a more viscous liquid with a similar smell. The difference is in use where the gel coat is applied directly to the mould without reinforcement and mainly provides a smooth, coloured finish to the outside of the hull. In contrast, the laminating resin provides the matrix within which the reinforcement is bedded. These and other components will be explained in the following sections.

50 years of reinforced plastic boats

Fifty years ago, if you wanted a yacht, it would be custom-built for you, as a one-off, usually by fastening together hundreds of separate hand-crafted pieces of wood. Most boats of any size, including working craft, were built this way. Only the well-off could afford them.

But the boat building industry was about to jump ship from wood to a novel ‘wonder’ material. As it was generally known, fibreglass offered the prospect of continuous monocoque structures that would start and stay watertight, along with ease of building the whole series of identical boats. So fibreglass/glass-reinforced plastic (GRP) went on to transform boat building from a small-scale enterprise steeped in wood and tradition to what is rapidly becoming a commodity industry.

Although Reinforced Plastics magazine first saw the light of day at about the time this boat building revolution was getting underway, the history of fibreglass boats extends a couple of decades further back still. According to US sources, Ray Greene, an employee of the Owens Corning company, produced a composite boat as early as 1937 but did not proceed further due to the brittle nature of the plastic used (it was most likely phenolic). Experimenters experienced other difficulties too. For example, when Basons Industries tried to produce a fibreglass boat in the early 1940s, no release agent was used, and the hull could not be extracted from the mould. Mould and hull were eventually disposed of by rolling them into the Bronx River!

All the materials needed were coming together during the 1930s. Glass fibres were known to the ancients. Still, mass production of glass strands only became possible from 1932 when a researcher with the Owens Glass company accidentally directed a jet of compressed air at a stream of molten glass and produced fibres. After Owens Glass joined up with the Corning company in 1935, the method was adapted by Owens Corning to produce its patented ‘Fiberglas’ (one ‘s’). Product researchers could see the potential for combining clothes of this material with plastic but had to wait a few years more for a suitable resin.

Advantages and Disadvantages of Boats Built in FRP

Advantages

• Reduction of maintenance
• No caulking, no leaks. Hulls are one continuous piece of FRP with no joints or gaps to allow water into the hull.
• No plank shrinkage when laid up. Wooden hulls suffer from plank shrinkage when brought out of the water and laid up in the sun. However, FRP does not shrink or swell, so leakage and re-caulking are avoided.
• Rot proof and resistant to borers. FRP is non-organic and will not rot. Therefore, like plastic, it cannot be eaten by marine borers.
• Corrosion and electrolysis reduced. FRP is inert. Like plastic, it will not rust.
• Simpler construction. Once a mould is made, identical copies of a hull can be made many times over and in a shorter time.
• Reduction of skill levels required once basic training is received.

Disadvantages

• Total dependence on imported materials and foreign currency availability.
• Choice of vessel fixed once the design is chosen and moulds made.
• Must retain a core group of qualified technicians.
• Fire and health hazards from chemicals.
• Large start-up investment.