Validation of External Moment Determination for the Shaft-Line of the S.A. Agulhas II

Full-scale measurements of shaft torque have been performed on several voyages of a polar supply and research vessel, the SA Agulhas II. Previous work has looked at the determination of the externally induced ice moments on the propeller to shed light on the expected loading conditions in the harsh Antarctic environments. This has been done by making use of a lumped mass model, measurements taken on the shaft-line and an inverse prediction algorithm. Thus the externally applied loads are determined through the internal measurements on the shaft-line. The work presented here is in an effort to assess the validity of the lumped mass model parameters used in the external moment determination process. Two methods of validation have been performed. The first is through the comparison of the lumped mass model to operational modal analysis data of the shaft-line, obtained during dry-dock operations in 2017. The second validation method that is considered relies on data recorded on board the SA Agulhas II during its 2018–19 Annual Relief Voyage to Antarctica. The shaft-line measurement system has been expanded to include the measurement of torque at a second location, further down the shaft. These two measurement locations are each used to determine the external loads and their results are compared. It was found that the results of the validation show correlation, albeit with some error, and that the developed method is valid for use in determining externally induced ice moments. However, there is room for improvement of the current external moment determination method.