Southeast Alaska Cruise Ship Underwater Acoustic Noise

Kipple, Blair

Between September 2000 and June 2001, the underwater radiated noise levels for six Southeast Alaska cruise ships were measured at the U.S. Navy's Southeast Alaska Acoustic Measurement Facility near Ketchikan, Alaska. The primary objective of this project was to quantify noise levels typical of large cruise ships common to Southeast Alaska. This group of ships included diesel-electric, direct-diesel, and steam turbine propulsion plant ships ranging in size from 23 to 77 thousand gross tons and from 617 to 856 feet in length. Ten-knot overall sound levels ranged from 175 to 185 dB relative to 1 microPascal at 1 yard with the highest one-third octave band level at 182 dB. The 10-knot sound level for the steam turbine ship was the lowest among the ships tested, but no ship was clearly the loudest or quietest at all frequencies. Propulsion system type and cavitation performance were important factors in cruise ship noise character. Diesel-electric ship noise signatures were dominated by noise energy from diesel generators and from electric propulsion motors in combination with frequency converters and diesel generators. Propulsion diesel and reduction gear noise were important contributors in the directdiesel ship's signatures. Turbine generator, propulsion turbine, and reduction gear noise were the most significant noise items in the steam plant ship's signatures. Each ship was tested at two speeds. The sound levels of two ships were strongly speed dependent while others exhibited less speed dependence. Differences in noise levels between speeds were typically due to changes in propulsion and cavitation noise contributions. This investigation indicates that a 10-knot ship speed limit in Glacier Bay (versus 20 knots) would, in general, result in reduced underwater noise levels, although the results also indicate there could be exceptions, particularly at speeds in the neighborhood of 15 knots. Only two ships were tested at speeds near 20 knots. Ship noise levels were measured at a range of 500 yards from each ship and were projected to 1 yard and 100 yards to examine the effect of range on perceived noise level. This factor was significant in terms of ranking importance of noise sources, ranking noise levels by ship, and in the degree of noise level dependence on ship speed. Comparison of noise levels at these ranges indicated that mid-frequency noise energy would typically be more important than low frequency energy at ¼ mile.

Southeast Alaska Cruise Ship Underwater Acoustic Noise

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