New Designs 31′ SD 31 Tri with Rigid Beams December 5, 2015 kurt 4 Comments I can’t believe that I have not posted this anywhere before , but all my searches here have not turned up anything on it. 31′ by 28′ wide. Plywood carbon beams. Can be built demountable. The set is almost done. CM plywood/epoxy for rapid building.