The performance of bow foils in irregular and oblique waves

Bow foils are an emerging energy saving device that utilise wave energy to improve the efficiency of ships operating in waves, through both a reduction in ship motions and the generation of additional thrust. To identify the performance of bow foils in oblique waves, this paper presents and compares experimental results from a series of free-running model tests, with and without a bow foil, with constant forward speed, in regular and irregular oblique waves. The experiments identify the effect of bow foils on the ship heave and pitch motions, shaft torque and revolutions and foil forces and motion, over a range of relative wave headings. The results, demonstrating the ITTC QNM method, show that the bow foil reduces the delivered power required to maintain a given speed in waves, and are effective across a range of heading angles, modal periods, and wave height once a threshold is reached. The results also verify the use of spectral approaches to predict the performance of bow foils in irregular waves using transfer functions and identify that the greatest power savings are achieved in head wave conditions. The presented results provide a holistic design methodology to predict and scale the performance of bow foils across a range of sea states.