Noise and vibration prediction and experimental verification on board a fiberglass motoryacht

Abstract

This paper briefly outlines the methodology normally adopted by the authors to assess the noise levels of a Motor Yacht during the preliminary design stage. The procedure is based on measurements carried out on board similar yachts and enables the determination of noise levels in the main accommodations, the engineroom, the wheelhouse, etc. This paper gives an example of the method for predicting noise levels for a 75 ton GRP Motor Yacht, 30.8 m long, 2 x 1440 kW MTU diesel engines, driving two 11 degrees inclined shaftlines at 2100 rpm. Cruising speed is 28 knots. To ascertain that noise levels were met, vibration and noise tests were carried out on board by a Classification Society. Its results, along with other additional figures obtained by the authors during further tests, are here reported in detail. The scope of these additional measurements was to check whether predicted noise levels agreed with measured values. A high vibration level was, however, recorded at the transom stern structure, definitely due to propeller excitation, which propeller was designed according to the best efficiency criterion. In order to lower the stern vibration level a new propeller was designed and installed. Its design, theoretical verification and performance predictions are illustrated in the paper. .