| CPC G01S 15/96 (2013.01) [G01S 7/521 (2013.01)] | 5 Claims |

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1. An attachment to be attached to an ultrasonic-wave transmitter/receiver for a fish finder, which is suspended from a cable, housing a molded ultrasonic transducer for transmitting and receiving ultrasonic waves with the bottom surface as an acoustic radiation surface characterized in comprising:
an acoustic lens having a flat surface and a convex surface located on the opposite side;
a holding member to hold the acoustic lens with the flat surface facing upward and to detachably hold the ultrasonic-wave transmitter/receiver so that the acoustic radiation surface is acoustically connected to the flat surface of the acoustic lens;
a horizontality-maintaining means to maintain the ultrasonic-wave transmitter/receiver and the acoustic lens horizontally,
a fitting hole provided on the bottom portion of the holding member so that a convex surface side of the acoustic lens with the flat surface facing upward is fitted thereinto and protruded downward from a bottom surface of the holding member; and
a water supply/discharge hole for supplying water into the holding member and discharging water from the holding member,
wherein the water supply/discharge hole is formed by widening a part of the fitting hole to form a gap to acoustically couple the acoustic radiation surface of the ultrasonic-wave transmitter/receiver to the flat surface of the acoustic lens via water; and
wherein the horizontality-maintaining means is provided so as to surround the holding member from the outer peripheral side, which is made of a material having a specific gravity smaller than that of water and is a buoyant body that horizontally maintains the ultrasonic-wave transmitter/receiver and the acoustic lens by a buoyancy acting on itself.
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