Boat Building

Making Scarph Joints in Plywood Panels

When your plywood sheets aren't long enough, they must be joined end-to-end.

Butt joints aren't strong enough. Backing blocks can cause problems when you try to bend the panels. CNC-cut puzzle joints work great – if you have a CNC cutter. So the good old scarph (scarf) joint is the standard solution.

Here's how to make one.

Where's the good wood?

When I built my little runabout fifteen (!) years ago, it was pretty easy to find suitable plywood. The boat was a Phil Bolger / Harold Payson design, and neither man was big on spending money where it wasn't required. Payson's advice was something along the lines of "well, she's glass-sheathed, so you don't need the fancy exotic plywood – just use local AC exterior ply with the boil-tested glue." He was right; after fifteen years there's no evidence at all of any kind of rot, deterioration, delamination or other trouble with Sunset Chaser's fir plywood hull.

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