Furuno CH-250 - Manual (Page 44)

2-26
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.
Sea surface
Sea surface
17˚
Tilt angle
indication
Sea surface
reflections
17˚
Figure 2-23 Sea surface reflections
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.
Own
ship
Other
ship
Wake produced
by other ship
Own ship's
screw noise
Own ship's
screw noise
Own ship's wake
(produced when
own ship turned)
Figure 2-24 Wake