Tuesday, December 30, 2008

Hull bottom scarfing

Scarfing wood is new to me, and when I did it for the mast it went pretty smoothly. But that was small strips only 2 inches wide. Now the hull floor has to have 2 full size sheets of plywood scarfed together perfectly and strong.
I took the idea of scarfing technique from John Welsford's "Backyard Boatbuilder" by staggering the two runs of plywood at the correct scarf slope then planing the ends to the slope needed. confusing? It might sound confusing but it's not. The picture shows the two scarfed pieces of plywood ready for assembly. The layers of plywood are a good guide for maintaining a straight line and an even slope.
You basically taper to a point the ends to be glued together. Then turn over and glue together on a flat surface so both sheets are "flat"
Once that's done I placed wax paper on a thin sheet of panel board on the floor and dry fitted the plywood. The whole thing is glued and wax paper laid on top. I used some weight to press the whole thing flat and true. The extra glue was sanded off some.
I had a hard time spotting the scarf line in the profile. It slopes down to the left in this picture.

Time: 3 hrs


  1. Hi Perry,

    I have done a practice scarf joint using the suggested technique with 12mm pine. It was not strong enough, I was able to with a fair bit of effort to break the joint. How accurate is the scarf joint to be? It sounds like you did a very good scarf joint if you cannot spot it. How thickened was the epoxy for gluing? My gluing of plywood on plywood so far has gone very well, as has my centreboard lamination.


    David Thomas

  2. My scarf joint for the bottom 1/2" plywood panel was at a ratio of 8:1 or 4" in length in this case. I layed down a good layer of epoxy glue to both sides, let sit for a short while so it could soak in the wood then placed it on the wax paper on the floor. the wax paper and weight was placed on top to press it down and make a good joint. Some people clamp but this did the trick. my scarf joint was pretty good, but making sure you have plenty of glue is most important. the plywood floor is bent down on the jig but nothing extreme in regards to a curve. I can't spot it mostly due to the epoxy glued being a semi transparent color and blending well. i'd say i have about 1/32" or 1/16" thick epoxy joint. hope this helps. Oh the epoxy glue for this was... just thick enough to not run hardly, like oatmeal perhaps.