Furuno CH-37BB, Operator'S Manual

Page: 26 / 71

2. SONAR MODE
2-10
2.9 Interpreting the Display
2.9.1 How the picture is painted
The wide sounding beam is emitted from the soundome at a certain tilt angle (see
hatched area in the figure below). The information (target echoes) obtained by this
beam is displayed in 45° sector of the screen. Thus, all directions around the boat are
sounded in 8 times of transmissions.
2.9.2 Bottom echoes
When the tilt angle is widened, the bottom echo illustrated below will appear on the
display. When the tilt is narrowed, the bottom trace becomes wider and weaker. By
observing the bottom condition on the display, the skipper can prevent net damage.
1) Flat bottom (Tilt angle 10° to 15°)
2) Flat bottom (Tilt angle 20° or more)
3) Sloping bottom (Tilt angle 20° or more)
Sounding beam Screen display
Tilt angle (θ) Tilt angle (θ) Tilt angle (θ)
Sounding beam
1 1
2 2
3 3
Soundome
Train
Tilt θ
45˚ 45˚ 45˚
1
3
2
4
5
6
7
8
Narrow tilt angle
Only half of
vertical beam
width captures
the bottom.
Bottom echo
displayed narrower
and in stronger
colors when
compared to (A).
Bottom echo
Shallow bottom
is displayed in a
strong color and
with a short tail.
The deeper
bottom echo is
displayed in a
weak color and
with a long tail. The deeper
bottom echo is
displayed in a
weak color and
with a long tail. The deeper
bottom echo is
displayed in a
weak color and
with a long tail.