Radiated noise characteristics of M/V OVERSEAS HARRIETTE, a modern cargo ship

Low-frequency ambient noise in the ocean is often influenced by radiated noise from merchant shipping. In an effort to quantify this noise, a series of extensive and carefully planned measurements were made of the radiated noise of M/V OVERSEAS HARRIETTE, a 25 525-deadweight ton 567-ft cargo ship powered by a direct-drive low-speed diesel engine. This ship and its power plant are typical of many modern merchant ships. The radiated noise data show high-level tonal frequencies from the ship's service diesel generator, main engine firing rate, and blade rate harmonics due to propeller cavitation. Directivity measurements taken at many angles under the ship indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate fundamental levels show good agreement with predicted levels. [Work supported by NRL.]