Sea Sail Boat

Around the mid 1960s, boats made out of glass-reinforced plastic, more commonly known as fibreglass, became popular, especially for recreational boats. The United States Coast Guard refers to such boats as 'FRP' (for Fibre Reinforced Plastic) boats.
Fibreglass boats are extremely strong, and do not rust (iron oxide), corrode, or rot. They are, however susceptible to structural degradation from sunlight and extremes in temperature over their lifespan. Fibreglass provides structural strength, especially when long woven strands are laid, sometimes from bow to stern, and then soaked in epoxy or polyester resin to form the hull of the boat. Whether hand laid or built in a mold, FRP boats usually have an outer coating of gelcoat which is a thin solid colored layer of polyester resin that adds no structural strength, but does create a smooth surface which can be buffed to a high shine and also acts as a protective layer against sunlight. FRP structures can be made stiffer with sandwich panels, where the FRP encloses a lightweight core such as balsa or foam. Cored FRP is most often found in decking which helps keep down weight that will be carried above the waterline. The addition of wood makes the cored structure of the boat susceptible to rotting which puts a greater emphasis on not allowing damaged sandwich structures to go unrepaired. Plastic based foam cores are less vulnerable. The phrase 'advanced composites' in FRP construction may indicate the addition of carbon fibre, kevlar(tm) or other similar materials, but it may also indicate other methods designed to introduce less expensive and, by at least one yacht surveyor's eyewitness accounts, less structurally sound materials.
Cold molding is similar to FRP in as much as it involves the use of epoxy or polyester resins, but the structural component is wood instead of fibreglass. In cold molding very thin strips of wood are laid over a form or mold in layers. This layer is then coated with resin and another directionally alternating layer is laid on top. In some processes the subsequent layers are stapled or otherwise mechanically fastened to the previous layers, but in other processes the layers are weighted or even vacuum bagged to hold layers together while the resin sets. Layers are built up thus to create the required thickness of hull.