Best would be a combination of ibashi and ash or cedar planks. Ibachi where it matters (leading edge) and ash or cedar to keep the weight below the maximum defined by the class rules. Use quarter sawn planks and turn them 90 degrees relative to each other to avoid warp. Glue them together to form a board using a strong two pot glue, and take it through a planing machine. Then shape it and add chamfer according to the rules and the drawing. Add a layer of glass fiber and epoxy and finish with UV resistant varnish or two pot paint. Before painting build up a sharp trailing edge with micro balloons and epoxy. Make a big hole for the bolt and fill it with micro balloons and epoxy before drilling the final hole. Or better use a bushing slightly wider then the thickness of the board.
However, most of us settle for a simple painted plywood board. This must be marine grade ply or it will break on your first trip.