Fig. 12. Measurements of efficiency versus coefficient of X-force. The blue data were first collected in a systematic matrix study over a predefined range of oscillation parameters. This data gathering was spread over about 1.5 years, which is common in conventional experimental procedures where the hydrodynamic characteristics and the models of control laws are determined before a vehicle design is carried out. The symbols denote the carriage speed, where x is U=0, o is 0.46, + is 0.83, and ^* is 1.34 m s^–1. The numbered dots denote trial numbers from the random search algorithm; green dots denote trials with a pitch bias greater than 5°, and red dots denote runs after which the bias had converged to less than 5°. Observe that from an arbitrary starting point, the algorithm rapidly reaches the point of highest efficiency for hovering as denoted by the x symbols. The search for maximum efficiency converges with any initial random selection of oscillation parameters. The rapid search method also works well when the fin is towed.