The Combatant Craft Engineering Department began, in the early 1980's, to evaluate a systematic series of propellers representing those available in the commercial market. The primary goal of the program was to generate "open-water" equivalent thrust and torque data, from full-scale trials, to improve propeller selection techniques for small craft and small ships, particularly at high speeds. The first phase of the program investigated three-bladed propellers with systematic variations in pitch ratio as well as propeller blade "cupping." Cupping has been a long-practiced, but ill-defined, art for fine-tuning propeller performance. The second phase, in 1987, expanded the series to include four-bladed propellers. In addition, the propulsion system of the test craft has been changed to achieve higher speeds, and therefore lower cavitation numbers.