4 Using the FISH 4500/4600
This section explains how to interpret the sonar displays, when and why to use the dif- ferent 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
4-1 Interpreting the display
The sonar displays do not show a fixed distance travelled by the boat; rather, they display a his- tory, showing what has passed below the boat during a certain period of time.
The history of the sonar signal displayed de- pends on the depth of the water and the scroll speed setting.
In shallow water, the echoes have a short distance to travel between the bottom and the boat. In deep water, the history moves across the display more slowly because the echoes take longer to travel between the bottom and the boat. For example, when the scroll speed is set to Fast, at depths over 1000 ft. (300 m) it takes about 4 minutes for each vertical line of pixels to move across the display, whereas at 20 ft. (6 m) it takes only about 15 seconds.
The scroll speed can be set by the user to display either a longer history with less fish information or a shorter history with more fish details. See section
If the boat is anchored, the echoes all come from the same area of bottom. This produces a flat bottom trace on the display.
The screen shot shows a typical sonar display with the Fish symbols turned Off.
Single fish
Large school of fish
Small school of fish
Bottom
Strength of echoes
The colors indicate differences in the strength of the echo. The strength varies with several factors, such as the:
•Size of the fish, school of fish or other object.
•Depth of the fish or object.
•Location of the fish or object. (The area cov- ered by the ultrasonic pulse is a rough cone shape and the echoes are strongest in the middle.)
•Clarity of water. Particles or air in the water reduce the strength of the echo.
•Composition or density of the object or bot- tom.
Note: Planing hulls at speed produce air bubbles and turbulent water that bombard the transducer. The resulting ultrasonic noise may be picked up by the transducer and obscure the real echoes.
Kelp / Weed
Soft bottoms such as mud, weed and sand show as narrow bands
Hard bottoms such as rock or coral show as wide bands
Bottom types
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
FISH 4500/4600 Installation and Operation Manual | NAVMAN | 15 |