Operation Manual

8120 Installation and Operation Manual33
the data to move across the window, whereas
at 20 ft (6 m) it takes only about 25 seconds.
The scroll speed can be set by the user to
display either a longer history with less fish
information or a shorter history with more
fish details (see section 17-3).
If the boat is anchored, the echoes all come
from the same area of bottom. This produces
a flat bottom trace on the window.
The screen shot shows a typical sonar
window with the Fish symbols turned Off.
The sonar pulse generated by the Instrument
transducer travels down through the water,
spreading outwards in a cone shape. The
cone width is dependent upon the frequency
of the pulse; at 50 kHz it is approximately 45°,
and at 200 kHz it is approximately 11°.
The differences in the cone width affect what
is displayed. (See section 8-3)
9-2 Interpreting the display
The sonar windows do not show a fixed
distance travelled by the boat; rather, they
display a history, showing what has passed
below the boat during a certain period of
time.
The history of the sonar signal displayed
depends the depth of the water and the scroll
speed setting.
In shallow water, the echoes have a short
distance to travel between the bottom and
the boat. In deep water, the history moves
across the window more slowly because the
echoes take longer to travel between the
bottom and the boat. For example, when the
scroll speed is set to Fast, at depths over
1000 ft (300 m) it takes about 2 minutes for
The appearance of echoes displayed are
affected by:
• The Instrument settings (see sections 17-3,
8-5 and 8-6)
• Echoes (different fish types, different
bottom types, wrecks and seaweed; see
section 8-2)
• Noise (water clarity and bubbles; see
section 8-2).
Cruise, Fishing and Manual Modes
The Instrument has three sonar operating
modes:
• Cruising mode: Use this when on the
move. The Instrument automatically
adjusts its settings to compensate for
water clarity and to display the bottom.
• Fishing mode: Use this when fishing.
The Instrument automatically adjusts its
settings to compensate for water clarity
and to best display fish, the bottom and
other details.
• Manual mode: Use this to fine-tune the
Instrument settings by hand. Best results
are often achieved in manual mode, but
practice and experience are required to
obtain the optimum settings for different
conditions.
For more information about modes, see
sections 8-5 and 8-6.
CAUTION
!
!
CAUTION
DANGER
WARNING
Use the automatic Cruising or Fishing
modes when learning to use the
Instrument or when travelling at speed.
A
C
B
D
A School of fish
B Hard bottoms such as rock and coral
show as wide bands
C Single fish
D Soft bottoms such as mud, weed
and sand show as narrow bands