Raytheon HSB L755, Owner'S Handbook Manual

Page: 115 / 224

Chapter 4: Fishfinder Operations 4-1
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Chapter 4: Fishfinder Operations
4.1 Introduction
Basic Fishfinder operation, including a description of the different display
options, was given in Chapter 3. This chapter helps you the get the most from
your Fishfinder. It describes how to fine-tune the image and use the controls to
get additional information.
This chapter covers the following topics:
• Interpreting and Adjusting the Fishfinder Image, including fish and bot-
tom indications, using the white line feature and adjusting gain (sensitiv-
ity).
• Viewing Data Windows
• Setting up and Using Alarms for fish, shallow water and deep water
• Using a VRM to Determine Depth and Distance from Boat of a particular
spot.
• Placing Waypoints
• Using the Man Overboard (MOB) function.
4.2 Interpreting and Adjusting the Fishfinder Image
The L755 and L760 Fishfinders use sound waves (sonar) to find fish and show
the bottom of a lake or sea. The transducer sends high-frequency sound waves
down into the water; these sound waves strike fish, the bottom, or other objects
in the water and return as echoes. The fishfinder interprets these echoes to
present an image of the fish and bottom.
The strength of echoes is indicated by shades of gray (L755) or different colors
(L760). You can use this information to determine the size of fish and the
bottom structure. Other objects in the water, such as debris and air bubbles,
also return echoes; these echoes are generally weaker than the fish or bottom
echoes and produce background noise or clutter on the Fishfinder display.
The Fishfinder provides controls to reduce the background noise and to adjust
the way in which echoes of different strengths are displayed. The color
Fishfinder (L760) also lets you select the background color and remove the
display colors for weaker echoes, refer to Changing the Brightness & Color
Settings (L760) on page 3-6 for details on these two functions.
The Fishfinder provides a White Line feature which helps to distinguish
between the bottom and fish (or other items such as weed) that are close to the
bottom.