Furuno gd-1700c Manuel D’Utilisation

4. VIDEO SOUNDER OPERATION 

 
 

Intensity difference
in water depth

Second bottom
echo

Rock base

Mud and sand

The zero line (sometimes referred to as the transmission line) represents the 
transducer’s position. 

Zero line

Shift

 

Echoes from the bottom are normally the strongest and are displayed in 
reddish-brown (color model) or darkest tone (monochrome model) but the color 
(tone on the monochrome model) and width will vary with bottom composition, 
water depth, frequency, sensitivity, etc. 
 
In a comparatively shallow depth, a high gain setting will cause a second or 
sometimes a third or a fourth echo to be displayed at the same interval between 
them below the first echo trace. This is because the echo travels between the 
bottom and the surface twice or more in shallow depths. 
 
The color (tone for monochrome model) of the bottom echo can be used to help 
determine the density of the bottom materials (soft or hard). The harder the 
bottom, the wider the trace. If the gain is set to show only a single bottom echo 
on mud, a rocky bottom will show a second or third bottom return. The range 
should be chosen so the first and second bottom echoes are displayed when 
bottom hardness is being determined.