April 13, 2009
Build a Dinghy: Part 7
The Summerbreeze design has a number of goals. Its to be a lightweight boat, under 70-lbs or so. It's a rowboat that can sail reasonably well. Its interior is kept wide open for sprawling space by using a leeboard instead of a centerboard or daggerboard to get upwind.
Its also designed to be easy and inexpensive to build. One way of keeping costs down is to use materials to the fullest, and designer David Beede accomplished that goal with Summerbreeze: it requires just two sheets of plywood.
How we made the 11'6" hull sides (planks) out of two 8-foot sheets--by using the scarf joint-- was detailed in the last post.Here we use the other common method of lengthening sheets of plywood in small boat construction: the butt block.
To make the bow of this boat, I cut two 32" long trinagles off the corners of a sheet of ply. These are flipped and attached to the front of edge of the sheet using butt blocks. The blocks are 3-inch wide strips of 1/4" (6MM) ply. Thats a 12:1 width to thickness ratio, the same as the scarf bevels, interestingly.
After cutting the triangles, I do a dry fit, and mark everything : centerlines, outlines, etc as shown in the photo. Next, I wet out the joints with straight epoxy and let it soak into the veneer for about ten minutes. This prevents the dry wood from sucking all the glue out of the joint. After the wet out has soaked in, I apply another coat of epoxy, this time with a thickening agent, to all the mating surfaces. This coat is the thickness of stiff batter. Then all the parts are laid in place and pressed in gently.
I used paint cans for clamping weights, using packing tape or other plastic on their bottoms to prevent them from sticking to the glue. Also note how I used the squeeze-out to form a filet (bead) along the butt blocks. Filets make the joint even stronger. You want squeeze-out becuae it shows you that you have complete glue coverage. But cleaning up the hardened epoxy is tough....