Composites are materials made up of two or more components combined so that the strength of the composite is higher than the properties of the individual components. Our canoes and kayaks are made of a reinforced plastic composite. This consists of fibre reinforcements embedded in a resin matrix. The resin used is thermosetting type, which is a plastic that cures from a liquid to a solid through a chemical reaction of its two components. Once this reaction occurs, the material can not be reformed.
Even when just adding glassfibre reinforcement, the tensile strength of the resulting composite is over 4 times higher than the tensile strength of the pure resin. The composite also becomes much more resistant to impact damage. The high strength achievable for lightweight construction is why fiberglass composites are used for almost all racing canoes and kayaks. Composite parts can also be built to withstand stresses in a particular direction by aligning the fibre reinforcements along that direction, and by adding extra fibres only in high stress areas. This saves additional weight by removing unnecessary material from areas with little stress.
Fabric selection is critical when building composite vessels. Select the wrong fabrics, and your boat may be too brittle, or heavier than it needs to be. There are many different materials available, with a variety of properties. Each material is also available in different weave patterns, and fabric weights. These fabrics are often combined together, with layers of different fabric types making up the finished laminate. Most of the fabrics described here are available from us in small quantities; please contact us for more details.
Fabric is just one part of the finished composite; it has to be bonded together with a suitable resin. Again, the wrong type of resin can have disastrous consequences - some types absorb water! The two most common types of resin are Polyester, and Epoxy. Polyester resin is the most widely used, since it is less expensive and easier to use. However, it is much weaker than epoxy, and can be excessively brittle. Polyester resin also has a tendency to shrink slightly when curing. All of the available car bodywork repair kits contain a type of polyester resin. This resin is designed to be easily sanded, and so is too weak to be used for boat repairs.
Epoxy resins are higher performance and more expensive than polyester. They are used in weight critical, high strength, and dimensionally accurate applications. The properties of epoxy resin from various manufacturers can differ a great deal - some are more flexible than others, or take longer to set, etc. To make the best possible boat requires a cured resin that is rigid without being too brittle. Not all fabrics are compatible with both resins - some types of Kevlar are coated so as to adhere better to eopxy resin, while polyester must be used with CSM to dissolve the starch binder.
So, once the choices of fibre and resin type have been made, these materials have to be combined and crafted into the shape of the boat. Composite boats are made in two parts; deck and hull, and then joined together. Each part is made in a female mould, also made of composite materials. The inside surface of the moulds are specially treated so that the parts to be made do not bond to the mould. Precut fabric reinforcement is placed one layer at a time into the mould and saturated with resin. When the part has achieved the desired thickness and orientation, it is left to cure. When it is demoulded, it will have the exact shape of the mould surface, and the mould can be re-used. The join at the seam is made with layers of Kevlar seamtape on the inside and outside, and fittings such as cockpit rim, seat, foam pillars, etc. are installed.
Still with us? If so, then hopefully you will have learnt something about the materials that we use. We choose composite over plastic to bring you the lightest, stiffest boats that we can. Learn a bit more about how we design and test our boats on the design page.