Furuno TS-331A - Manual (Page 37)

3. ECHO SOUNDER OPERATION
29
3.3 Using the Echo Sounder Image to Monitor Trawl
Location
If the ground rope is positioned in the coverage area of the sounding beam it is
displayed as a line almost parallel with the transmission line. If a fish school
appears between the transmission line and the ground rope it can be considered
to be entering the trawl.
Height of
Trawl
Opening
Fish School
Ground rope
of trawl
Bottom
Transmission line
Echo sounder display