While walking along the north end of Lake Union last night Katya and I ran into a couple assembling a homemade sectional plywood sailboat. The builder has a background in engineering and designed the boat to be able to store it in a small space, such as a condominium storage unit. He lives nearby and transports the boat on a cart.
The construction is marine grade plywood with fiberglass tape/epoxy along the joints, and metal strips along the sheerline. Metal plates and bolts are used to join the sections together at the sheer. Two cables run from the bow to the stern under the hull to hold the sections together. Each section is constructed with air chambers outfitted with plastic plugs for draining/decompressing. The bow is split into two sections so that it can nest into the forward (daggerboard) section. Note the rubber insulation strips at the corners of the forward section to protect the corners when the bow sections are nested.
The length overall is 15 feet. The mast and sails were salvaged from a smaller 11 ft sailboat that the builder found on CraigsList. Katya and I were on our way to watch A Clockwork Orange at the Fremont Outdoor Theatre so, unfortunately, we couldn't stick around to see the boat complete. Apparently, it takes at least 30 minutes to put together.
Home-built sectional boats have been around for quite a while. Check out this catalog of plans from the April 1940 issue of Popular Science. For a couple very interesting sectional kayak designs, check out Dick Mahler's stitch and glue plywood 3-piece Pygmy Arctic Tern 14 and sectional skin-on-frame Greenland kayak built by Lodro Dawa of Monkcraft Kayaks.