Raymarine L1250DRC, Owner'S Handbook Manual

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Chapter 6: Sonar Operations 6-1
In
trod
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Chapter 6: Sonar Operations
6.1 Introduction
Basic Sonar 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.
Note: Many of the parameters on the HD Series Fishfinders have both manual
and automatic modes. The automatic setting takes advantage the hardware’s
advanced digital technology. As a result, the sounder typically performs bet-
ter in automatic mode than in manual.
For better performance, Raymarine recommends that you select AUTO
mode wherever it is an option.
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 to a particular
spot
• Placing Waypoints
• Using the Man Overboard (MOB) function
Note: The settings described in this chapter are retained when the unit is pow-
ered off. However, there is a one-minute delay from the time you change the
setting to when the DSM250 places it in memory. If you power down the
sounder less than one minute after making a change, the setting is lost.
6.2 Interpreting and Adjusting the Fishfinder Image
The HD Series 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 different colors. 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.
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