Models for representative noise spectra for different classes of ships have been developed by the U.S.
Navy. The Research Ambient Noise Directionality (RANDI) model (Wagstaff 1973; Schreiner 1990;
Breeding 1993) uses ship length and speed as well as an empirically derived power law to determine the
broadband (5-500 Hz) spectral level for various classes of vessels. Peak spectral densities for individual
ships range from 195 dB re µPa2/Hz @ 1 m for fast moving supertankers, to 140 dB re µPa2/Hz @ 1 m for small fishing vessels. Source-level models have been also developed for the propeller tonal blade lines, occurring at 6-10 Hz for most of the world’s large merchant fleet (Gray and Greeley 1980). Small vessels do not contribute significantly to the global ocean acoustic environment, but may be important local sound sources. Examples of noise levels for whale-watching boats are presented by (Au and Green 2000) and (Erbe 2002). A recent study of noise levels from small powerboats suggests peak spectral density levels in the 350-1200 Hz band of 145-150 dB re 1µPa2/Hz @ 1 m (Bartlett and Wilson 2002).