The cause of the severe propeller excited broadband vibration on a twin screw ship's stern was investigated in a cavitation tunnel using conventional modelling methods. At first sight the results did not indicate anything untoward about the stern and propeller designs tested, apart from some unusual cavitation patterns in the propellers' slipstreams. The fluctuating pressure levels on the model hull varied considerably depending on the propeller designs and loading conditions used in the tests, but these did not provide an explanation for the vibration on the ship. Some unusual patterns in the relative levels of the harmonic pressures on the stern were noticed in addition to the presence of a large cavitation disturbance in a propeller trailing vortex that was captured in a single frame of a video recording. This latter observation led to a plausible explanation for the broadband vibration on the ship's stern.
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