: Hmm...have to look that one up, not sure if Rushton's laps were glued or not.
: With conventional lapstrake planking the laps are left unglued and
: unsealed and are completely watertight. Only takes a tiny bit of water to
: allow the bare wood edges to swell against each other to keep them that
: way since they arn't allowed to separate.

According to a couple of sources, Ted Moores and a bio of Rushton, the constant swelling and drying led to cracking of the thin strips. Rushton solved that by using narrower strips (2 inch rather that 4 inches or wider) and sealing things with varnish. The Rushton bio had copy from a sales flyer of his in which he mentions that the joints between the strakes were sealed with his varnish, and fastened with clenched copper nails between the ribs. I suppose we'd use epoxy as a sealer today. The wood didn't swell and shrink, so it didn't crack. That was a big deal for canoes which would be taken in and out of the water. larger boats which stayed wet didn't have the cracking problem because they didn't dry out.

: With modern plywoods and epoxy
: you can make a glued lap construction with very few frames that's very
: light, just takes a whole bunch more time shaping the planks than we'd
: spend shaping strips.

Thomas Hill's book "Ultralight Boatbuilding", shows this lapstrake construction with 1/8th inch (3mm) marine plywood. Where the "planks" overlap the hull is about 1/4 inch thick --same as a strip-built boat.

Hill starts with planks cut from his plywood sheets which are maybe 4 inches wide and 8 feet long. His molds are made like the frames for SOF kayaks, with "ribbands" running the length of the boat. We'd probably call those chines or stringers. His method of gluing down one edge of these plywood planks, then using a router with with a pattern cutting bit running along the ribbands to trim the excess material seems to be a pretty quick operation.

I suggest a similar technique for making plywood panels to cover the frame of a SOF kayak--as opposed to using fabric to skin it. Instead of using a router and pattern bit, I just run a pencil line along the chine (ribband) remove the panel, and cut on the line.

Since a hull made with Hill's technique uses fewer panels than a similarly sized boat would use thin strips, and since the overlapping of the strakes eliminates the need for rolling bevels, or cove and bead, I think this would take less time, not more. Working with planks made from plywood would also eliminate the time needed for ripping strips and planing them to thickness.

Plywood thickness is pretty even already. Scarfing up two sheets of plywood gives me almost 16-foot-long "strips' which are knotfree, without a lot of the wood turning to sawdust, too.

Hill, by the way, doesn't use glass on the inside of his boats, either. Very little on the outside either, for that matter. He adds a layer of Dynole, glass, or something similar on the bottom of the boat, in the "football" area, just for ding resistance.

Haven't actually had the time to build anything this way yet, so I can't say it is so, tho. Right now it is just my opinion.

PGJ