Silk scarfing and first glue up
The addition of a knob-stop and angling the bar clamp allows the guide rail to be repositioned without clamping. This small change increased efficiency. An important technical detail of this method of scarfing is having enough uncut edge surface on which to rest the rail. The final panel dimension is 40”, but these were left at 48” so that the 7 1/4” rail had enough room on the waste side of the panel. The only way of using this method if an entire board needed to be scarfed would be to add a temporary scrap piece, or strategically leave strips in select locations to support the rail. After these scarfs were completed, the boards were cut to width with the track saw.
The video depicts the major-domo of scarfing for this boat — a 6” scarf on 3/4” stock. While the 3” scarfs needed for 3/8” material can be quickly removed by the router, these doubly long and deeper scarfs require the removal of significantly more material, so slower passes are a must. A few rough passes with the Rotex sander set on grind mode with 80-grit paper smoothed out the joint face, but still left the cells rough and open to absorb epoxy.
This set of scarfs completes those needed for the bottom panels.
Now that the scarfing of the bottom panels is complete, the first set are joined. I started with the aft and middle 3/4” sections. As per the manual, a straight edge (a freshly cut piece of remaindered 3/4” plywood) was screwed to an underlying piece of 3/4. The straight edge helps ensure the glue-up is straight.
Plastic and packing tape beneath the scarf prevent epoxy from sticking to the straightedge and the board to which the pieces are clamped. The top clamping board is also covered in plastic and tape.
Several coats of straight epoxy were applied to each scarf face with a foam roller. After allowing the epoxy to soak in, another coat is added until it no additional epoxy would be absorbed by the end grain. Then, a thick slurry of epoxy and glass fibers was applied to one face of the scarf and the pieces were joined. A straightedge ensured flatness across the scarf.
Despite minimal squeeze out, I do not believe the joint is starved. The ‘clamping board’ used to apply even pressure over the joint received nails every 4”. I added more nails than specified because it seemed that the edges of the board were very slightly lifted… Can’t hurt.
Did I mention?
One of the space limitations I am working around is the need to store our 16’ Snow Goose in one of the garage bays. The boat is rolled out of the garage to make way for working, then rolled back at the end of the day. This necessitates some careful planning and placement of materials. Here. the boat trailer straddles the newly scarfed blank as they slowly cure. I’ll check the progress of the joint in a couple of days and then get the next set glued up. At some point. I will need to use the jig as a workbench for gluing the 3/8” sections to the 3/4” ones because the garage is not large enough to house the 28’-long final assemblies.
