There are two basic kayak designs; sit-in and sit-on. A sit-on kayak is becoming popular with fishermen and divers because of the ease of mounting and dismounting the craft in deep water. Building a kayak can be as complicated or as easy as you want to make it. The foam and fibreglass, sit-on kayak is one of the simplest kayak designs. A foam core, covered in several layers of fibreglass, and paint will get you on the water cheaply and quickly.
Cut the shape of your hull into the styrofoam with your hacksaw. Take your time and be careful to leave the top of the foam flat. Maintain the basic dimensions of the original foam in the centre half of the foam to keep the stability. Carve out an indention in the top of your foam core with a knife. The indention should be three inches deep and just wide and long enough for your posterior and legs.
Attach fibreglass cloth to the foam core with your staple gun. Pull the cloth tight being careful to avoid wrinkles. Cover the entire foam core with cloth. Place staples every six inches to hold the fibreglass cloth securely against the foam. Trim the cloth as necessary with your scissors to remove wrinkles. Staple the edges of each cut to the foam core.
Cover the fibreglass cloth with epoxy, using your putty knife. Apply a thick layer of epoxy over the entire craft. Lay another layer of cloth to the wet epoxy. Smooth the resin covering the cloth with your putty knife and allow the epoxy to dry completely. Apply a second thick coat of epoxy to the kayak and allow it to dry completely. Smooth the fibreglass with the heavy grit sandpaper on your palm sander using a circular motion to avoid cutting grooves into the fibreglass.
Spray the kayak with three coats of yellow paint by holding the can eight inches from the surface and shooting short bursts of paint, while moving the can in a side-to-side motion. Allow each coat of paint to dry completely before applying the next. Lightly sand each coat of paint by hand with extra fine grit sandpaper, before the next application, to shine the finished paint job.
Apply a thin coat of epoxy to the kayak with your putty knife. Allow the epoxy to dry and sand smooth with your palm sander. Paint the kayak with three coats of yellow paint, allowing each to dry completely before the next application. Lightly sand each coat of paint by hand with the extra fine grit sandpaper using a light circular motion. Launch your kayak, sit on top of the craft and try it out.
Enclosing a foam core with fibreglass will give you an unsinkable craft. Even if it breaks into a number of pieces will become an emergency flotation device that could save your life.