Slamming and dynamic loads of marine propellers operating under partially submerged conditions

This paper presents an investigation into the dynamic loads acting on the blades of propellers working in partially submerged conditions. In partially submerged conditions, the average thrust and torque is significantly reduced, while the variations in thrust and torque are much increased. The current study investigates whether impact-type loads on the propeller blades in surface-piercing condition might result in large torque loads – significantly larger than the torque in normal, full power operation. In the first stage of the study, a single-bladed half submerged propeller was tested at low impact angles, to measure the loads experienced if an impact situation should occur. Further, a more realistic condition was added using a four-bladed propeller operating in half submerged conditions at propeller low impact angles. The test results for the four-bladed propeller showed that even at extremely high pitches and varying advance speed, the disturbance to the free surface caused by the passing of the previous blade created sufficient disturbance to the free surface to prevent high torque loads. Nonetheless, damage in the shaft system could be caused by fatigue as a result of high amplitude dynamic loads, even if the magnitude of this loads could not be classified by slamming.