Small-boat source level estimates in a fjord environment

Small vessels contribute to noise in the marine environment and it is of interest to measure radiated noise levels of such. This paper presents measurements of radiated noise from small leisure boats (lengths 16 to 23 ft) conducted at a shallow water site in a fjord environment. The measurements used a bottom-deployed tripod with three hydrophones, and a laser instrument for boat range and speed estimation. Data were processed for source levels in one-third octave frequency bands from 0.1 to 1.6 kHz and using the ANSI/ASA standard for distance normalization. For boats moving at speeds 4 to 6 km, source levels varied by up to 20 dB between boat types. Estimated broadband source levels were 8 to 22 dB lower than for merchant vessels previously measured in the same environment.