A composite material (commonly shortened to 'composite') is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure.
Composites are now an established part of the marine industry for the construction of fishing vessels, pleasure boats, high-speed lightweight craft such as ferries and patrol craft, and larger Naval vessels. Advantages that have contributed to this include their high specific (i.e. per unit mass) strength and stiffness, the ease with which seamless complex shapes may be formed, and their high chemical and environmental resistance.
The composites used in the marine industry are almost exclusively laminated Fibre Reinforced Plastics (FRP’s), with the great majority consisting of hand-laminated, low-fibre-fraction, polyester-reinforced woven and discontinuous glass fibres, with sandwich construction used for weight critical applications. However, the introduction of new production processes such as 'resin infusion' and the increasing uptake of more high performance fibres such as carbon mean that this is changing rapidly in some sections of the market.
See Eric Greene's excellent book Marine Composites for more information.