Sea Surface Reflections; Wake - Furuno CSH-5L/CSH-8L Operator's Manual

6.3

Sea Surface Reflections

To reduce sea surface reflections, set the tilt angle to 5 or more so that the
upper edge of the sonar beam does not hit sea surface, or adjust the TVG
functions. When the sonar is used with a narrow tilt angle, the sea surface
reflections cover a large area (up to 300 m to 400 m) as illustrated below.
Tilt: 0˚
Tilt: 5-6˚
6.4

Wake

A wake produced by own ship or another ship can be a strong reflecting object
when the sonar is used with a narrow tilt angle. As the wake appears on the
screen as a thick continuous line, it can be easily distinguished from a fish
school. On the other hand, the wake contains a lot of air bubbles which
attenuate ultrasonic energy, making it often difficult to sound beyond the wake.
Own
ship
Sea surface
Sea surface
Sea surface reflections
Other
ship
Own ship's
screw noise
Wake produced
by other ship
6. INTERPRETING THE DISPLAY
Own ship's
screw noise
Wake
Tilt angle
indication
Sea surface
reflections
Own ship's wake
(produced when
own ship turns)
6-3