Seabed Conditions - JRC FF50 Instruction Manual

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Seabed Conditions

After some experience, you will begin to understand and recognize different
seabed conditions (sand, mud, rocks, etc.), by paying attention to variations in
the sea bottom return being drawn on the display. When water depth and
sensitivity settings remain the same, the display may show variations in the sea
bottom return image caused by changing bottom conditions.
Echoes appear at the right edge, adjacent to the range scale, and scroll left
across your display. Each time the Fish Finder transmits and receives, old echoes
shift to the left to make room for the new echoes. As your vessel moves, an image
of the bottom contour and fish echoes that you pass fill your display.
• When the seabed is hard and flat like a mirror, only the beam directly under the
transducer is reflected back to the transducer. This echo appears on your display
as a narrow bottom line, characteristic of hard, sandy seabeds.
• When the depth is shallow and the seabed very hard, a second echo can appear
at exactly double the depth of the true seabed echo.
• When the seabed is soft (an abundance of seaweed or mud), the bottom line on
your display appears thicker. This is because the top surface of the sea weed or
mud sends a weaker echo than the bottom itself and also because waves
returning to the transducer may be slightly delayed.
• When the seabed is made up of coral, wrecks, or rock piles, the irregular surfaces
and various angles of the seabed return closely spaced echoes. The bottom line
on your display appears with irregular long tails.
Seabed Displays
The FF50 high-resolution display provides accurate representations of
various bottom conditions.
Soft
(Mud)
Hard
(Sand)
Rocks
Figure 6-2