Outboard engines had existed since the early 1900s, but real momentum arrived when Ole Evinrude introduced his lightweight Evinrude Light Twin Outboard, the ELTO, in 1920. By 1927, more than 500,000 outboards had been sold, and annual sales were climbing sharply. The rise of affordable, speedy and reliable engines democratized a sport that wealthy thrill-seekers once dominated. The American Power Boat Association formalized outboard racing rules in 1924, and participation surged. That enthusiasm inspired experiments at the edge of aviation. In 1929, Russell J. Robertson patented a “waterplane”—an airplane-like craft powered by an outboard-driven pontoon. A joystick controlled the elevator and ailerons, while foot pedals moved the rudder. At the 1930 National Regatta on the Connecticut River, an ELTO outboard pushed one such water plane past the crowds, adding a…