Operation Manual

74 A-Series display - User reference manual
6.3 Interpreting the Fishfinder image
Bottom indications
The bottom usually produces a strong echo. These images indicate
the bottom conditions as follows:.
The dark layers indicate a good echo; the lighter areas weaker ech-
oes. This could mean that the upper layer is soft and therefore
allowing sound waves to pass to the more solid layer below.
It is also possible that the sound waves are making two complete
trips – hitting the bottom, bouncing off the boat, then reflecting off
the bottom again. This can happen if the water is shallow, the bot-
tom is hard, or gain is set too high.
Factors influencing the readout
When an object is detected, it is displayed on screen as a mark.
The quality and accuracy of the display can be influenced by a num-
ber of factors including boat speed, depth, object size, background
noise and transducer frequency.
Boat speed
The fishfinder’s reading of the bottom and other objects is affected
by your relative speed. Slower speeds return flatter, more horizontal
marks; as your speed increases, the image will tend to thicken and
arch, until at high speeds the bottom resembles a double line on the
fishfinder display.
Object depth
The closer the target to the surface, the larger the mark on the
screen. individual target depths can be shown using the Target
Depth ID function.
Water Depth
As sea depth increases, signal strength decreases, resulting in a
lighter on-screen image of the bottom.
Object size
The larger an object is, the stronger its return on the fishfinder dis-
play will be.
However, the strength of return from fish depends upon the species’
swim bladder, rather than the body size.
D6855-2
A hard bottom (sand) produces a thin line
A soft bottom (mud or seaweed cover) produces a wide line.
The dark layer indicates a strong signal.
A rocky or uneven bottom or a wreck produces an irregular
image with peaks and troughs