Acoustic signatures of small boats measured in controlled lake conditions

Abstract

Measurements were conducted under controlled conditions at Lake Hopatcong, NJ, to compare acoustic signatures of various small boats. The tested boats included: an outboard-driven Panga, a multiple-outboard driven go-fast boat, an electric drive vessel, a personal watercraft (PWC), and two small outboard-driven rigid hull inflatable boats (RIBs). Stevens Passive Acoustic Detection System (SPADES) was used for acoustic measurements and the specially developed “Portable Vessel Data System” (PVDS) was used to record vessel position, speed, shaft RPM, and vessel orientation. Vessel acoustic Source Level measurements were conducted by comparing the recorded vessel acoustic signals with a signal generated by a calibrated emitter from the same point. Dependencies of acoustic signatures on boat speed and loading were also investigated. For several vessels, the Source Level decreased when its speed increased. Analysis of tonal components in the vessels acoustic signatures with Detection of Envelope Modulation on Noise (DEMON) allowed to determine the number of engines per boat and even the gear ratio for transformation of shaft rotation to the propeller rotation. [This work was supported by DHS S&T.]