Garmin 188c User Manual

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The area covered by the transmitted sound waves is determined 

by the cone angle of the transducer and the water depth. The wide 

cone angles (40°) associated with low frequencies (50 kHz) provide 

a large coverage area for finding fish within a coverage width that 

is approximately 2/3 of the water depth. However, this also means 

that wide cone angles produce less bottom detail and resolution. 

As shown in the drawing on the near right, the 40° cone angle 

produces a coverage area of approximately a 20-foot diameter 

circle at a 30-foot depth. 
The narrow cone angles (10°) associated with the high frequencies 

(200 kHz) provide better bottom resolution and crisper detail, but 

cannot show a large coverage area for finding fish. The 10° cone 

angle provides a coverage width that is approximately 2/10 of the 

water depth. As shown in the drawing on the far right, the 10° cone 

angle produces a coverage area of approximately a 6-foot diameter 

circle at a 30-foot depth. 
Dual frequency mode combines both frequencies to get the best 

coverage area and contour/depth readings.

Coverage 

Diameter

Coverage 

Diameter

Depth

Depth