Interpreting The Bottom Structure; Factors Influencing Target Display - Raymarine E120W Reference Manual

Chapter 6: Using the Fishfinder

Interpreting the bottom structure

The bottom usually produces a strong echo. These images indicate the bottom
conditions as follows:.
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
The dark layers indicate a good echo; the lighter areas weaker echoes. 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 bottom is hard, or gain is set high.
The Fishfinder provides various features to help you interpret the fishfinder picture.

Factors influencing target display

The shape and size of this mark is influenced by a combination of factors:
Boat speed
The shape of the target changes along with your speed. Slower speeds return flatter,
more horizontal marks. As your boat's speed increases, the target will tend to thicken
and arch slightly; until at fast speeds the mark resembles a double vertical line.
The depth of the target
The closer the target to the surface the larger the mark on screen.
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