: Working without a kit- it would be fairly easy to make a jig to cut
: interlocking puzzle-type scarfs in plywood like kits use. There
: can be advantages over a through-the-thickness scarf. In a
: through-the-thickness scarf there is much more surface area for
: gluing, but this also makes an area stiffer than the surrounding
: plywood, so it is easy to have an unfair curve. In a puzzle
: scarf the glue area is greatly increased over a butt joint, but
: it is nowhere near as great as a through-the-thickness scarf. On
: the other hand, it will not introduce any unfair curves.

: Obviously, a CNC router can cut a puzzle scarf, and having it cut
: in this manner will greatly increase the ease and accuracy of
: construction for a home builder buying a kit. This is probably
: the point of a joint like that. In the case of either type of
: joint, the scarf will be covered by fiberglass. So how critical
: is strength? How strong is strong enough? How critical is joint
: flexibility? Has anyone had a joint failure or fiberglass stress
: (turn white) at a puzzle joint? Is anyone with a puzzle joint
: subjecting their kayak to high stress paddling like surf and
: rock gardens with plenty of wipe-outs?

: Inquiring minds want to know.

: m

I've never seen any unfairness in plywood scarfs, don't see the need to play with puzzle joints. I use West system's Scarfer to make my cuts in plwood, works just fine. I know this tends to scare some people and it's indeed different making a 4' long scarf across the width of the plywood. I dowel the two pieces together then weight the joint when I'm epoxing them, keeps the joint straight. It was considerably easier when I had the big shop, the floors were all thick wood so I could just screw the plywood to the floor, hard to do that now with the concrete floors :)

Bill H.