Every beast must have a skeleton, and a boat is no different. The discs are 1/4" Plexiglas, the top post is 1/4" galvanized threaded rod, and the bottom two are 3/4". I wanted to make sure the keel was heavier that the topside. The micro-controller board is in place between the center two ribs. This rib structure was designed/built for the single-hull design. I have to remake them for the current double hull design.