Furuno FSV25S, Operator'S Manual

Page: 40 / 163

2. HORIZONTAL MODE
2-8
2.4.4 Tilt angle for surface fish
The sound emitted from the sonar transducer forms a beam with a width of approxi-
mately 10° in the vertical direction (vertical beam width at -6 dB). The tilt angle indi-
cates the angle between the centerline of the beam and the horizontal plane. Then, if
the tilt angle is set to 0°, the centerline is parallel with the sea surface and one half of
the emitted sound goes upward, toward the sea surface.
This causes one half of the emitted sound to be re-
flected toward the transducer and displayed on the
screen as sea surface reflections. When the sea is
calm, since the sound is reflected just like a light
hitting a mirror at a low incident angle, it propagates
away and the sea surface reflections become neg-
ligible.
However if the sea is not calm enough, they will be-
come dominant and interfere with observation of wanted echoes. To minimize these
sea surface reflections and to search for schools of fish on the surface effectively, the
tilt angle is usually set between 4° and 5° so the upper portion of the beam becomes
almost parallel with the sea surface. When the sea is rough, the tilt angle is slightly
increased to lessen the affect of sea surface reflections.
2.4.5 Suitable tilt angle
The figure below illustrates the relationship among tilt angle, depth and detection
range. Refer to it to find out the suitable tilt angle for a given depth/detection range.
Tilt angle 0°
Sea surface
Tilt angle 4 - 5°
Sea surface
10°
11°
Vertical width of sonar beam
Depth (m)
Tilt angle setting: relationship between tilt angle and detection range
Tilt 0
°
(0°-5°)
Tilt 5
°
(0°-10.5°)
Tilt 15
°
(9.5°-20.5°)
Tilt 15
°
(4.5°-15.5°)
In grey
Range(m)
100
(200)
200
(400)
300
(600)
400
(800)
20(40)
40(80)
60(120)
80(160)
100(200)
200(400)
10 °
17 m 17 m
100 m
300 m
200 m
35 m 35 m
52 m 52 m
11 °
19 m 19 m
100 m
300 m
200 m
39 m 39 m
58 m 58 m
Vertical beam 10° Vertical beam 11°