Changes

There are two types of resin: laminating and the previously mentioned gelcoat. “Marine General Purpose” Isophthalic or Neopentyl Glycol polyester resin is used commonly.

To make a mould, you start with a plug in the exact shape of the hull or hull component. The plug is disposable, and can be made from a variety of materials. The exterior of the plug is highly finished.

Moulds are typically used for limited production. For series produc-tion, construction is done using just a plug. With a plug, fibreglass is laid up over the outside of the plug, with a roving layer last, and then hand finished with a gel coat. Today, plugs can be cut using multi-axis robotic milling machines driven by CAD cutting files.

Hand lay-up is not common today, for reasons of efficiency and environment. Special guns that spray resin and chopped glass fibres into the mould have replaced hand lay-up. A more recent technique, vacuum infusion, uses a vacuum bag over the mould to en-sure consistent quality.<ref>Fiberglass World, http://www.fiberglass.com/</ref> <ref>Pacific Northwest Pollution Prevention Resource Center, http://www.pprc.org/</ref>

Fibreglass components are made with either a single-skin or a sandwich construction. Single-skin construction uses alternate layers of continuous and woven roving that are saturated with resin and allowed to cure. Typical glass-to-resin ratios are 30:70. Unidirectional and biaxial reinforcing materials can increase strength while eliminating stress deformation, reducing weight and increasing the glass-to-resin ratio to 50:50, which is better.

Sandwich construction was introduced to reduce material cost. It uses a foam-core material, plywood or balsa wood between two layers of fibreglass. Wood of any kind is not recommended because it readily absorbs water, which will delaminate the sandwich.