Select the plan for the type of boat you want to build and either make arrangements to rent the female mold for the hull or obtain detail drawings to construct your own one-time use mold. Detail drawings are available at boat yards and online. Ask around your local marina for suggestions as well.
Decide on the type of fiberglass material you will be using for your project. Fiberglass mat consists of random fibers that are puncture-resistant but heavy when cured with resin. Roving has a more specific weave and is easier to work with but less puncture-resistant. Cloth is very tightly woven and puncture-resistant and is lighter than mat or roving. However, it is also more costly than either mat or roving.
Choose the resin and catalyst based on whether the hull will be used in fresh or salt water, its long-term exposure to UV light, your budget and the working characteristics of the material. The plans you purchased should come with specific recommendations. Your supplier can also offer advice, and those who have rented molds often leave suggestions as well.
Dress in protective clothing and have acetone handy in case curing resin gets on your skin as it heats to extreme temperatures and can cause burns. Set floor fans down for ventilation.
Apply one or more layers of mold release to your custom-built or rented hull mold. This release agent will allow you to pull your hull out of the mold.
Apply a thin gel coat with a brush or roller, compatible with your selected resin type, to the surface of the mold. This gel coat can be clear but is usually colored to the desired finished color of the boat hull.
Mix the resin and catalyst according to directions. It will begin to heat up and cure immediately and, depending on heat and humidity, can set very fast. Stir the mixture slowly and evenly to avoid air bubbles. You will repeat this process often as you layer the material.
Saturate pieces of cloth or roving on a flat table covered with mold release and transfer them to the mold to layer a large hull. A more common fabricating technique for smaller hulls is to lay fiberglass material in the hull mold then apply the resin to position it in place, Dab the material with brushes, roll resin with foam rollers and use squeegees to saturate and fit it firmly to the shape of the hull mold. You will have to work quickly because the resin cures and hardens rapidly.
Repeat the layering process, allowing the resin to cure in between layers. The boat design you purchased or the mold you rented will come with recommendations on how many layers thick you should make the hull.
Use standard woodworking tools, such as wood rasps, saws and carbide sandpaper, to trim and sand the final cured hull edges.
Remove the hull from the mold.