Model propulsion tests in head and following waves of a bulk carrier

The results of self-propulsion measurements in calm water and regular head and following waves, under different propeller loading conditions, are presented. The experimental measurements were performed in the large towing tank at the Marine Technology Centre in Trondheim. The model was a 1:32 scale replica of a 200-meter bulk carrier, equipped with a 4-bladed, moderately skewed propeller measuring 210.9 mm in diameter. Results for wave-added resistance and thrust, propulsive coefficients, ship motion RAOs (Response Amplitude Operators), effective wake fraction, advance ratio magnitudes and amplitudes, and efficiencies ( η 0 , η H , η R and η D ) were computed. Firstly, resonance at a wave length to ship length ratio of 1.2 in head waves was generally observed in all results. Particularly in head waves, this lead to a significant increase in the wave added resistance. The thrust deduction fraction t was higher in waves than in calm water, but the variation in the different wave conditions was small and difficult to see a systematic trend, so a constant thrust deduction fraction in waves were assumed in the analysis. Due to the differences observed between the thrust deduction factor in calm water and in waves, the added thrust coefficient presented higher values than wave added resistance coefficient. The increased resistance in head waves of wave length to ship length ratio of 1 and longer lead to an increase in propeller loading, leading to larger thrust coefficient K T , lower advance number J and lower propeller efficiency η 0 . The effective wake fraction showed a slight reduction in head waves and a slight increase in following waves. In following waves, the added thrust was small, leading to small changes in the average values of the propulsive coefficients. However, the amplitudes of thrust, torque and advance number were significantly larger in following waves than in head waves, something that might be of importance for propeller shaft and engine dynamics. Regarding ship motions, overall, lower ship speeds produced larger motions. Also, in following waves, a consistent increase in motion (heave, surge, and pitch) was observed with increasing wavelength.