Detailed Measurements on a Modern Cargo Ship
Arveson and Vendittis present a set of very detailed measurements on a modern cargo ship. Extensive measurements were made of the radiated noise of M/V Overseas Harriette, a bulk cargo ship (length 173 m displacement 25,515 tons) powered by a direct drive low-speed diesel engine, a design representative of many modern merchant ships.
The image shown below describes the spectral levels of the noise generated by the vessel at various speeds and propellor rotation rates.
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. Radiated noise directionality measurements indicated that the radiation was generally dipole in form at lower frequencies, as expected. There were some departures from this pattern that may indicate hull interactions. The blade rate source level (174 dB re 1 µPa at 9 Hz at 16 knots) agreed reasonably well wilh a model of fundamental blade radiation previously reported by Gray and Greeley, but agreement for blade rate harmonics was not as good.
The paper notes that noise from merchant ships elevates the natural ambient by 20-30 dB in many areas; the effects of this noise on thc biological environment have not been widely investigated.
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