THE UNDERWATER NOISE EMITTED BY FISHING B OATS

The underwater noise emitted by fishing boats is one of the main noise sources in coastal fishing grounds. This paper intends to investigate the underwater noise emitted by fishing boats, by means of measuring both drifting and cruising noise for small trawlers and medium purse s einers. The spectrum of noise when drifting showed some harmonics (lin e component spectrum) of basic frequency which corresponded to the mai n engine and generator revolution pitch. The noise at cruising showed a powerful continuous component spectrum above 50 Hz frequency zone to the propeller influence as well as line components spectrum. It domin ated when applied to full speed ahead and astern. The sound spectrogra m of underwater noise emitted by fishing boats when cruising showed fu rthermore doppler phenominon and interference. These functions at crui sing were influenced by distance from noise source, depth, reflection number, main engine and generator revolution, and cruising speed.