Bill, good luck with your project, sounds like you have some awesome paddling ahead. My only input is a philosophical one. Maybe we should just boycott the plywood industry untill they start making 20' plywood. I've observed for years the aviation and marine home-built communities fret over scarf joints. The only reason those sheets are 8 feet long is because house walls are 8 feet tall. They are now making 30 and 40 foot long engineered beams, why can't we have say 2' x 20' marine ply in 1.5, 3.0mm and so on. Is there a wood products engineer out there? Is it just too small of a market? Anyway I plan on building some sort of kayak this winter, and I read all these postings with great interest trying to build input before I start. At some point I've got to just start cutting wood. It will probably be strip-built and one of the main reasons is those darn scarf joints. Good Luck, Kirby