NorthStar Navigation EXPLORER 657 - Manual (Page 32)

Northstar Explorer 657 Installation and Operation Manual 32
8-2 Interpreting the display
The sonar displays 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 display
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 data to move across the display,
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 display.
The screen shot shows a typical sonar display
with the Fish symbols turned Off.
Strength of echoes
The colours indicate differences in the strength of
the echo. The strength varies with several factors,
such as the:
• Size of the fish, school of fish or other object.
• Depth of the fish or object.
• Location of the fish or object. (The area
covered by the ultrasonic pulse is a rough
cone shape and the echoes are strongest in
the middle.)
• Clarity of water. Particles or air in the water
reduce the strength of the echo.
• Composition or density of the object or
bottom.
Note: Planing hulls at speed produce air
bubbles and turbulent water that bombard the
transducer. The resulting ultrasonic noise may
be picked up by the transducer and obscure the
real echoes.
The scroll speed depends upon the water depth
and scroll speed setting. See sections 17-3 and
section 8-2, for more information.
The appearance of echoes displayed are affected
by:
• the 657 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).
Cruising, Fishing and Manual Modes
The 657 has three sonar operating modes:
• Cruising mode: Use this when on the move.
The 657 automatically adjusts its settings to
compensate for water clarity and to display
the bottom.
• Fishing mode: Use this when fishing. The
657 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
657 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.
! WARNING
Use the automatic Cruising or Fishing modes
when learning to use the 657 or when
travelling at speed.