False Echoes - Furuno FSV-85 MARK-2 Operator's Manual

4. SLANT MODE
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.
4-34
Sea surface
reflections
Wake produced by
other ship
Wake produced by
other ship
Wake produced by
own ship when it
turns