Boat designers with experience in steel and aluminum will immediately notice that most fibreglass materials have lower strength and stiffness values than the metal alloys they are used to working with. Because glass fibre materials are much lighter than metals, thicker laminates can be designed so that the stiffness can match or exceed that of metal hulls.

   There are a number of types of fibre used in reinforced plastics but glass fibres are the most common because they are inexpensive to produce and have relatively good strength to weight characteristics.

   With the exception of chopped strand mat (CSM), reinforcements used in a marine glass fibre application usually utilize bundles of fibres oriented in distinct directions such as glass cloth and woven roving. Some are aligned in a single direction others multidirectional and the strength of the laminate will vary accordingly.

   There is a considerable variety of glass reinforcements but we are mainly interested in what is known as E-Glass or electrical grade glass that was originally developed for insulators, for electrical wiring, and is now used almost exclusively as the reinforcing material commonly known as fiberglass. E-glass is the most common reinforcement used in marine laminates because it is relatively inexpensive, has good strength properties and resistance to water degradation.

   Another glass fibre known as S-Glass is a structural glass typically used in higher strength applications. It has a greater tensile strength and stiffness than E-Glass and in general, demonstrates better fatigue resistance but at a considerably higher cost which means that it is limited to selected applications.

    There are other types of fibre such as carbon fibre and graphite fibre, used as reinforcement and known as Multi-axial Engineering Fabrics or just plain Engineered Fabrics which, when knitted stitched or woven into materials, include names such as Double Bias, Biaxial and Tri-axial Fabrics and Woven Fabrics and so on but these are specialised materials which probably won’t concern you. There is even an aluminised fibre used primarily for its cosmetic appearance which has a thin coating of aluminium to create a highly reflective surface but, so far, this is not used in boatbuilding.

   When you decide to build a fiberglass boat you should, primarily, be guided by the boat’s designer and the technical knowledge of your material suppliers. Don’t be confused by the vast array of materials on the market, most will never concern you. The majority of readers of this book will be concerned with building a strong, practical boat, so unless you are considering a specialised race boat, lightweight flyer or multihull, you can concentrate on E-glass and use the more traditional fibreglass boat building materials and methods.