Marine Propeller and Rudder Cavitation Erosion from Full Scale Observations and the Results of a Research Programme

Abstract

Ship components such as propellers and rudders are commonly operating in cavitation inducing conditions, therefore they are destined to experience the destructive effects of the phenomenon. Consequently, significant noise, as well as vibrations are commonly reported from ship operators. In addition, propellers and rudders also suffer from cavitation induced erosion, which in some cases can develop even within a few hours of operation, thus the expected service life of those components can be negatively influenced. This paper aims to present an ongoing research programme conducted by the Marine Engineering department of City, University of London which is oriented towards the evaluation of ultrasonically induced cavitation erosion in relation to materials commonly used in propellers and rudders, such as grade DH36 steel, stainless steel 254 and cupronickel 70-30, both from a quantitative and qualitative point of view. As such the relevant experimental procedures that were followed, including mass loss and acoustic emission measurements as well as microscopic and fractographic observations, along with the most important findings, are presented and explained. Results indicate that the proposed experimental procedure can form a baseline upon which efficient and effective evaluation of different materials in relation to ultrasonically induced cavitation erosion can be conducted. Moreover, the development of an acoustic emission-based cavitation erosion monitoring system for rudders, oriented towards the evaluation of erosion both in terms of intensity and location, is also presented. Results, from measurements conducted on small specimens and a reduced-scale model rudder, indicate that the system can potentially be used as means of cavitation erosion monitoring in full scale rudders.