The Scarab 18 is easy to build in either foam sandwich or plywood.
The following building notes are for a foam sandwich, flat panel boat using foam/polyester construction. This boat can also be built using plywood. You should use epoxy resins when building with wood. There are some benefits and set backs to both materials. With foam construction the foam must be removed around exposed edges and backfilled with solid filler and wherever anything is bolted through the foam panels (to prevent crushing the foam). Foam boats don't sweat, generally weigh less and have a higher resale value than plywood boats. These design notes are not complete. We will update them as we progress with the building of the second Scarab 18. We hope these building notes help you decide on your new project.
The boat can be built using:
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 bolted together. 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.
- Plywood scarfed to the right length.
- Foam sandwich panels you can make using foam, glass cloth and resin (epoxy, polyester or vinyl ester).
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 bolted together. 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.
To calculate the cost of making your own panels the following measurements may help. This is for one panel (1220mm x 2175mm).
This size panel was used to build a Scarab 18 or a Scarab 650. Foam thickness and glass size and amount of resin will
change for larger boats.
- 1 10mm klegecell foam sheet
- 4.6 litres polyester resin
- 4.5 metres of 450 biaxial glass
- 4.5 metres peel ply
- Calculate and multiply by the total number of panels specified in the material list.
Building the main hull
The frame is set up and levelled.
LOFTING
After the panels are made (pre-made sheets) or scarfed plywood the hull panels are drawn up using the off-set dimensions. It is much easier to stack the sheets and 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 using staples. The panels are joined along the edges using soft metal strapping for foam sandwich or copper wire for plywood, sometimes nylon cable zip ties can also be used.
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.
Because the bottom three panels are hard to get to when the boat is upright, they can be filled and sanded before turning
the boat.
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. It also makes the boat low enough so it is easy to work inside. (Details of the cradle
are supplied if this is preferred).
The main-hull is now taped inside.
The stem can be finished as in the diagram below. The inside of the bow 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.
©2010 Team Scarab