Saturday: Scarf & Glue

Finally, time to start the real construction. Since I bought the kit, I get to skip over what for most builders is the first big task: cutting out the pieces. My first step is to join several pieces together to form the bottom and sides of the boat.

Since the boat is 17' feet long, and plywood (with few exceptions) can only be had in 4' x 8' sheets, several pieces must be glued together to form much longer pieces. There are a few different ways to do this, but the preferred method is to "scarf" the pieces; this means to plane or cut short "ramps" on the edges to be joined, which will then form a larger surface area for glue bonding than if we simply "butt" the pieces together. Cutting a good scarf is non-trivial, however. Again, I am glad that I bought the kit: Graham's CNC machine has cut elegant "step scarfs" on all the edges to be joined.

I choose to do the sides first; I don't have enough room to do both sides & bottoms at the same time. I've laid two sheets of 1/2" plywood end to end, then stapled plastic over the entire surface. I then lay out the sides (three pieces each) and "dry fit" them. The middle piece has its scarfs cut in the same direction, so I lay these pieces such that the ramps go "down" and fasten to the plywood w/ three drywall screws at each end.

First "issue": since I'm laying 1/2" ply on the floor, the side pieces are of 1/4" okoume ply...and I only have 1 5/8" drywall screws, I can only sink the screws about half way. The pre-drilled holes (some of which are missing anyway) are too close together if I'm going to lay a 1x8 board across the join for clamping...the partially-sunk screws will get in the way. So I leave the screw holes on the center piece as they are, but on the two pieces to either side I drill new holes a few inches further away from the join (being careful to drill into the ply below as well.)

Last thing: I prepare my 1x8 cross pieces, wrapping them in plastic. (These are recycled from the kit box's framing lumber.) And I make a little trip with my wagon to where (behind the woodshed) I have a stack of old cinder blocks I'm not using. These will be weights to put on top of the cross pieces.

Mix the epoxy -- little experience here, so I make a guess as to how much. Turns out to be a little too much, but not a lot. Using the "fast" hardener -- which, at the temps I'm working at (low 60's I think) isn't really all that fast (I did do a test run earlier). I "wet out" the scarfs on all pieces, then go back to the epoxy station and add a bunch of cab-o-sil to the epoxy until it has the consistency of honey. Go back, spread the thickened mixer on two scarfs, turn over the un-fixed piece and mate it carefully to the fixed (middle) piece. Check twice, thrice...then sink my drywall screws. Do this 4 times; lay the cross pieces across the joins; carefully place two cinder blocks on each cross piece. Phew!