Boat plans for the 16 designed to heavy weather and sea conditions, this 16′ sea power ensures a calm ride so you and your crew won’t get thrown around when the. Welcome to spira international home-built boat plans. spira international offers a wide variety of different power, rowing, and sailing skiffs, dories, and other boat. Links to boat plans some free boat plans, boat building information including plywood stitch and glue. full range of boat plans from sophisticated yachts to plywood.