That design was a quick throw together. I am not in the boat design biz. As to construction.. I have used 4mm okume ply for tortured wood construction in the past (a-cat and 18Sq) but for strip planking I think it would be to thin to get a proper tongue and grove joint. As to the beam issue I am using 4" (125+/-) .069 wall 6061 T6, these beams are leftover from an 18Sq project from 20 years ago. I am working on a oval carbon tube design to fit to my boat next year. Coming from a 18Sq background (and having not sailed a cat with a crew in a very long time) I am unfamiliar with the dynamics of an F-16 so any thing I suggest should be take with a few grains of salt.
