Inspired largely by this
Instructable, here is my rough, quick and dirty attempt at building a sailing beach toy.
Step 1: Frame
The photos explain this fairly well. Some scrap Pinus Crapiata and 9mm exterior plywood make up the basic frame. I assembled these parts using self drive wood screws, a couple of roofing screws and some horrible, sticky, black polyurethane adhesive.
When you build yours, either go with a triangular structure or the same Tee shaped frame I have done, but with hollow box beams of larger section than I have used here or just better timber. While this frame seems adequate for my weight and mild conditions, the torsional stiffness of both the longitudinal and lateral members is slightly lacking. It is mildly disconcerting to have your seat twisting around as you sail along. I reckon probably the best way to go for most people would be a triangular structure welded up from steel RHS.