Propeller‐ and Thruster‐Induced Noise and Vibration

Abstract

Abstract Propellers are often the root cause for inboard noise and vibration, causing discomfort for crew and passengers. In some cases, propeller‐induced vibrations may even be large enough to cause fatigue damages to the ship structure. The pressure field induced by the propellers is transmitted through the surrounding water and may cause disturbance to marine life. Several norms and standards exist for inboard ship noise, vibration, and waterborne noise emission. The vibratory forces and noise from the propellers can be divided into two main parts according to path of transmission. The shaft forces are transmitted from the propeller to the propeller shaft system, while the hull surface forces are a result of the pressure field transmitted from the propeller through the water to the hull surface. Vibratory shaft forces are caused by the fluctuating load on the propeller blades due to the spatial variation in the wake field. The hull surface forces mainly originate from transient cavitation on the propeller blades. There are several ways of predicting forces and induced pressure field from propellers. Theoretical models are becoming more advanced as the computational capacity increases. It is now feasible to apply more general viscous flow solvers to compute most features related to vibratory forces from propellers. These methods are expected to replace the traditional ship model tests in the future. Ship vibration resulting from the propeller excitation forces depend on the response of the vessel to the applied forces; henced, the magnitude of the excitation should always be evaluated with respect to the vibration level it causes. The same evaluation should also be made when addressing the propeller as a noise source. Reduction of vibratory forces and noise from propellers may be in conflict with the efficiency of the propulsion system. Consequently, it is important to have a good way to control the on‐board vibrations and noise to find the best compromise between fuel consumption and onboard comfort level.