You should use epoxy resins when building with wood. There are some benefits and set backs to both materials. Foam must be removed around exposed edges and back filled. Foam boats don't sweat, generally weigh less and have a higher resale value than plywood boats.
We hope these building notes help you decide on your new project.
Making the panels
The boat can be built using
Plywood scarfed to the right length.
Foam sandwich panels you can make using foam, glass cloth and resin (epoxy, polyester or vinyl ester).
We choose to make our own panels for convenience and cost. We use low stryene emission polyester resin (but you can use epoxy resin). Use Klegecell foam or similar.The panels can be made to length before glassing.
If you use the tables as described in general info they are joined together using clamps or bolts. The foam is glued together to the right length (polyester/epoxy resin and aerosil works well) and the foam is attached to the table using drywall screws. When the glue is dry remove the screws and fill the holes with resin and filler (Q-cells). Roll the glass out over the foam and smooth out. Resin is spread beginning at one end and only covering as much as you can work at a time. Make sure the glass is covered and compacted into the resin. Cover with peel ply and smooth out the air bubbles. It is much easier to work epoxy because of the longer set up time. Panels can be trimmed with a knife before the resin hardens.
When making the panels we found that the foam can change size with temperature difference. Because epoxy takes longer to harden the panel can change dramatically leaving wrinkles in the panel so constant temperature must be maintained for about 12 hours. There is not this problem with polyester. It is much quicker to harden and there does not seem to be any warp in the panel. Polyester resin does shrink more than epoxy so the panel may look distorted slightly but this will be corrected when the other side is glassed. We have found that by using polyester resin we can glass both sides of the panel in one day which saves time.
Building the main hull
The frame is set up and levelled.
LOFTING
After the panels are made (pre-made sheets) or scarfed plywood or the hull panels are drawn up using the off-set dimensions. It is much easier to cut more than one panel at a time. Plywood sheets can be stapled together and foam can be screwed together using drywall screws. This way you only have to draw the panel once and it saves time.
The main-hull panels are attached to the frame and screwed in place with gyprock (drywall screws). With a plywood boat the panels can be attached to the frame with staples.
Joints on the main-hull are filled, sanded and faired. The bottom three panels are covered with double bias glass cloth over the joints. This provides extra protection if the boat is pulled onto the beach. The other joints are taped with double bias tape.
The main-hull is lifted off the frame and turned over. The boat is allowed to rest on a piece of plywood on the floor eliminating an extra building frame.
The main-hull is then taped inside.
The stem can be finished as in the diagram below. The inside of the stem is sanded and pre-wetted double bias glass is laid in as shown. When the glass hardens resin mixed with aerosil is poured into the gap. This should be in sections as the resin will generate considerable heat with a possibility of catching fire.
Bulkheads are tacked in place and then filleted and taped. Inspection port holes are cut to allow access to the water tight compartment.
Foam glassed both sides is difficult to bend over the foredeck so we use a modified method to to construct the curved deck. Uncovered foam is used and then glassed after it is bent. Scraps of foam are screwed on the outside of the mainhull to support the deck foam. The foam is then bent over the stringer and attached to the scrap foam. The glass cloth is wetted out. When the resin hardens the deck can be removed and the scrap foam cut from the deck. The deck is then glassed on the inside. This step is simplified with a plywood boat because the plywood can be bent over the curve.
