Dock next turned to the question of outboard motors. In 1951, he orchestrated the first successful down-run of outboard motorboats through the entire Grand Canyon. The 1951 "Marston Motorcade" consisted of two outboard motorboats and three stock Chris-Craft Speedsters. The 18-foot aluminum hull outboard motorboat June Bug was piloted by Jimmy Jordan and the second boat of the same design, the Twin, was piloted by Rod Sanderson. The two outboards were powered by twin 25-horsepower Evinrude outboard motors. While the June Bug completed the cruise, not far below Separation Canyon, the gearshift on the motor of the Twin gave trouble, and the boat was taken in tow, much to the disgust of its crew.Martin, Thomas C., (2012). Big Water Little Boats: Moulty Fulmer and the First Grand Canyon Dory on the Last of the Wild Colorado River. Flagstaff, Arizona: Vishnu Temple Press, p. 67, Marston, Otis R., (2014). From Powell To Power; A Recounting of the First One Hundred River Runners Through the Grand Canyon. Flagstaff, Arizona: Vishnu Temple Press, pp. 492–95
