Our bases consist of a 2” x 5” cylinder that is welded to a ¼” flat plate. The cylinder is high strength, 6061-T6 aluminum with 1/8” walls. These bases can be fixed mounted to a gunnel or flat surface using 4, 5/16” stainless hex head bolts. Bolt hole pattern is 3 ½” X 3 ½”. Backer plates come with our planer masts and rocket launchers at no extra charge and are available at low cost for all other systems. Custom base sizes are also available. Please call us with your custom requests.