Sea Surface Reflections - Furuno CH-250 Operator's Manual

Sea surface reflections

To reduce sea surface reflections, set the tilt angle to 5 or higher, so the upper edge of the
sonar beam does not hit the sea surface, or adjust TVG. When a decreased tilt angle is used,
sea surface reflections cover a large area as illustrated below.
Wake
A wake produced by own ship or another ship can be a strong reflecting object when a
decreased tilt angle is used. As the wake appears as a thick continuous line, it can be easily
distinguishes from a fish school. A wake contains many air bubbles which attenuate ultrasonic
energy, making it difficult to sound beyond the wake.
Other
ship
Own
ship
2-26
Sea surface
17˚
Sea surface
17˚
Figure 2-23 Sea surface reflections
Own ship's
screw noise
Wake produced
by other ship
Figure 2-24 Wake
Tilt angle
indication
Sea surface
reflections
Own ship's wake
Own ship's
(produced when
screw noise
own ship turned)