Navigation and Seamanship

6.1.3.2. Transducer

The function of transducer is same as in the case of echosounder.

SONAR is able to train(rotate) the transducer through 360^o and also be tiltable, usually from about +5°(up) slightly towards the sea surface and to -90°(down) vertical down to the sea bed. In order to achieve this, the transducer is mounted in gimbals and in order to avoid the turbulent layer and aerated water along the hull of the ship, it is lowered to about 1 m below the ship’s bottom when in operation. The transducer assembly must be able to withstand considerable mechanical stress when the vessel is under way and must be retractable when not in use, when docking, or in very shallow water; also to avoid fouling fishing gear, such as purse seine. Some larger sets have a built-in safety feature which causes the transducer to be retracted automatically when the set is switched off. The control for the transducer is usually mounted, with the recorder, in the wheelhouse of the vessel.