Hydropod: An Onboard Deployed Acoustic–Visual Device for Propeller Cavitation and Noise Investigations

Conducting noise trials with big merchant vessels could constitute serious economic and time losses for the ship operators. This study aims to introduce an experimental acoustic–visual device enabling economical and cost-effective noise trials in full scale. Noise emission and dynamics of propeller cavitation are investigated on a research vessel equipped with a customized submerged device called “Hydropod” that consists of hydrophones and a high definition, wide-angle underwater camera. Previously conducted noise trials following the international standards with an off-board hydrophone array are utilized for the validation of the adopted approach. The comparisons between the Hydropod measurements and conventional noise trial measurement results have shown promising correlations, except for a self-noise hump present in the noise spectra of the Hydropod measurements. Furthermore, by taking advantage of the replacement of the conventional propellers of the catamaran with a set of new profile technology (NPT) propellers, additional trials were conducted using the Hydropod. This enabled interpretation of the relative performance of both sets of propellers in terms of acoustics and cavitation extent. The NPT propellers were superior compared to the conventional propellers over the cavitation extent and resulting acoustic emissions.