Navman Using the Fish 4432/4433, Interpreting the display, Strength of echoes, Bottom types

4 Using the FISH 4432/4433

This section explains how to interpret the sonar displays, when and why to use the different frequencies and how fish are detected

and displayed.

It also describes Gain and Range and shows examples of some of the different sonar displays. Also see section 1-2 How the FISH 4432/4433 works.

4-1 Interpreting the display

The sonar displays do not show a fixed distance	Strength of echoes
travelled by the boat; rather, they display a	The colors indicate differences in the strength
history, showing what has passed below the
	of the echo. The strength varies with several
boat during a certain period of time.
	factors, such as the:
The history of the sonar signal displayed	• Size of the fish, school of fish or other object.
depends on the depth of the water and the
	• Depth of the fish or object.
scroll speed setting.
	• Location of the fish or object. (The area
In shallow water, the echoes have a short
	covered by the ultrasonic pulse is a rough
distance to travel between the bottom and the
	cone shape and the echoes are strongest in
boat. In deep water, the history moves across
	the middle.)
the display more slowly because the echoes
	• Clarity of water. Particles or air in the water
take longer to travel between the bottom and
the boat. For example, when the scroll speed is	reduce the strength of the echo.
set to Fast, at depths over 600ft it takes about	• Composition or density of the object or
2.5 minutes for each vertical line of pixels to	bottom.
move across the display, whereas at 20ft it	Note: Planing hulls at speed produce air bubbles
takes only about 4-5 seconds.
	and turbulent water that bombard the transducer.
The scroll speed can be set by the user to	The resulting ultrasonic noise may be picked up by
display either a longer history with less fish	the transducer and obscure the real echoes.
information or a shorter history with more fish
details. See section 3-2 Setup > Sonar.
If the boat is anchored, the echoes all come
from the same area of bottom. This produces a		Soft bottoms
flat bottom trace on the display.
		such as mud,
The screen shot shows a typical sonar display		weed and
with the Fish symbols turned Off.		sand show
		as narrow
		bands

Single fish	Hard bottoms
	such as rock
Large	or coral
	show as wide
school of
	bands
fish
Small school
of fish	Bottom types
Bottom	Mud, weed and sandy bottoms tend to weaken
	and scatter the sonar pulse, resulting in a weak
	echo. Hard, rocky or coral bottoms reflect the
	pulse, resulting in a strong echo. See section
	5-3 Sonar Bottom display.

17 NAVMAN FISH 4432/4433 Installation and Operation Manual