Navigation and Seamanship

6.1.1. Introduction

SONAR (an acronym for Sound NAvigation and Ranging) is an acoustic equipment that works with the principle of underwater sound propagation like echosounder. It is useful to navigate the vessel safely and to find the fish shoal in the distance from a vessel. Also it can measure the echo characteristics of "targets" in the water. Originally it was called as “ASDIC” which stands for “Allied Submarine Detection Investigation Committee” developed for the naval welfare as a device to detect sub marine during the World War I. In World War II, the Americans used the term SONAR for their systems. Later, this is used for finding fishes and become indispensable equipment for the successful and profitable fishing operation. Principle is similar to echo sounder. In case of echo sounder, the ultrasonic sound waves are transmitted vertically downward, but in SONAR, the sound beam can be directed to any angle by turning the transducer to any bearing around the vessel to 360º.

Sonar operates in much the same way as an echo sounder and has the same four main components the transmitter, the transducer, the receiver and the recorder or display. SONAR is capable of producing pulses of different duration principle of SONAR is the same as the principle of Echosounder. The difference is that the transducer of Echosounder operates vertically and the transducer of SONAR operates horizontally or in any lateral direction