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 designs that are simple to build, rugged and seaworthy.. Build a flat bottom jon boat plans . these plans are to build a flat bottom fishing jon boat. fisherman who like to work the shallow backwaters and weed patches on lakes and rivers will find this flat-bottom scow-type boat an ideal craft.. Free boat plans for the backyard home builder, plywood and wooden sailboats, rowboats, dinghies motorboats.