False Echoes - Furuno FSV-85 Operator's Manual

4.22.3

False echoes

Sea surface reflections
In the half-circle display, sea surface reflections appear as a thick line extending
across the own ship mark regardless of tilt angle. When the sonar is used with a nar-
row tilt angle, the sea surface reflections cover an extended area as illustrated below.
Wake
A wake produced by own ship or another ship can be a strong reflecting object when
a narrow tilt angle is used. As the wake appears as a thick continuous line, it can be
easily distinguished from a school of fish. A wake contains many air bubbles which at-
tenuate ultrasonic energy, making it difficult to sound beyond the wake.
Sea surface
reflections
Wake produced by
other ship
4. SLANT MODE
Wake produced by
other ship
Wake produced by
own ship when it
turns
4-35