Forward Speed Prediction of a Free-Running Wave-Propelled Boat

Wave-propelled boats utilize submerged flapping foils to convert wave energy directly into propulsion. For platforms that are solely propelled using submerged flapping foils, predicting the forward speed is challenging as it is time varying and dependent on the coupled responses of the wave-induced hull motions (surge, heave, and pitch) and the foil flapping motion (driven by the wave-induced hull motions and incident wavy flow). To ascertain the free-running response of wave-propelled boats, this article presents a hybrid discrete time-domain numerical model and experimental results from a prototype wave-propelled autonomous surface vehicle (ASV) with forward and aft (tandem) flapping foils. Results from a series of free-running experiments in regular head waves, over a range of wave frequencies for three different foil locations, are presented and used to validate the numerical model. The model was found to show good agreement with the experimental results, capturing the coupled dynamics of the vessel and foils and oscillating forward speed, over a range of wave frequencies and foil locations. The model and results provide a valuable insight for the design of wave-propelled boats.