Spectral analysis of the underwater acoustic noise radiated by ships with controllable pitch propellers

This paper presents spectral analyses of the underwater noise radiated by ships equipped with controllable pitch propellers. The noise measurements were performed at sea for three different ship's types. Each ship passage was characterized by a specific combination of propeller rotational speed and propeller pitch, allowing to investigate the variations of the radiated noise spectrum at different settings of the pitch-RPM combination law. Neglecting the low-frequency contributions, the focus is on the analysis of the broadband patterns in the range 100 Hz to 4 kHz A parameterization derived from a basic spectral pattern is adopted: the noise spectrum shape is approximated with a flat level magnitude up to a reasonable frequency followed by a logarithmic decay. An investigation of the relationship between the considered parameters and the actual ship condition is proposed along with a comparison with the predictions provided by classic Ross and Whales-Heitmeyer ship noise models.