Furuno CSH-84, CSH-83 manual Tilt angle for surface fish, Tilt angle and sea surface reflections

Tilt angle for surface fish

Sound emitted from the sonar transducer forms a circle-shaped beam with a width of approximately 12 degrees in the vertical direction (vertical beam width). The tilt angle is indicated by the angle between the center line of the beam and the horizontal plane. Then, if the tilt angle is set to 0 degrees, the center line 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 reflected toward the transducer and displayed on the screen as sea surface reflec- tions. When the sea is calm, since the sound is reflected just like a light hitting a mirror at a narrow incident angle, it propagates away and the sea surface reflections become negligible.

However if the sea is not calm enough, they will become domi- nant and interfere with observation of wanted echoes. To mini- mize these sea surface reflections and to search surface fish schools effectively, the tilt angle is usually set between 5 and 6 degrees so the upper portion of the beam becomes almost paral- lel with the sea surface. When the sea is rough, it is often set to a little larger angle.

	Surface
Tilt angle 0°	12°
	Surface

Tilt angle 5-6°

12°

Figure 2-2 Tilt angle and sea surface reflections

2-5