Specmar aluminum catamaran hulls are either symmetrical or asymmetrical in design. a symmetrical hull consists of two basic v-bottom hull structures.. Boat plans for a 23′ trailerable lobster boat designed for welded aluminum or plywood construction.. Designs available in steel…. steel is an excellent boatbuilding material, proven in use worldwide. however, due to the relatively high weight compared to other boatbuilding materials, and the care required in the design stage with regard to hull development, structural integrity, stability, and balance, the plans used to build a steel boat should be intended specifically for use with this.