Furuno FCV-582L manual Surface Noise/Aeration, Surface noise/aeration

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3.4 Surface Noise/Aeration

When the waters are rough or the boat passes over a wake, surface noise may appear near the zero line. As surface turbulence is acous- tically equivalent to running into a brick wall, the bottom echo will be displayed intermit- tently. Similar noise sometimes appears when a water temperature difference (thermocline) exists. Different species of fish tend to prefer different temperature zones, so the ther- mocline may be useful to help identify target fish. 200 kHz tends to show shallow ther- moclines better than 50 kHz.

In rough waters the display is occasionally in- terrupted due to below-the-ship air bubbles obstructing the sound path. This also occurs when the boat makes a quick turn or reverses movement. Lowering the picture advance speed may reduce the interruption. However, reconsideration of the transducer installation may be necessary if the interruption occurs frequently.

Surface noise

Caused by aerated water

Thermocline

Figure 3-4 Surface noise/aeration

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Contents Color LCD Sounder First Edition APR Safety Instructions Table of Contents Iii FeaturesForeword Word to FCV-582L OwnersUser Menu Menu TreeDisplay Unit System ConfigurationPrinciple of Operation Control Description Operational Overview22.6 C 12kt NL1 200k Indications, MarkersNormal display Turning On/Off the PowerAdjusting Tone and Brilliance Selecting a DisplayDual-frequency display 49.628.2 Marker-zoom displayData display Bottom-zoom display36.4 Bottom-lock display69.4 m Graphic displayBasic range selection Adjusting the GainSelecting Display Range Selecting data or graphic displayHow it works How to enable automatic operationAutomatic Operation Selecting Picture Advance SpeedMeasuring Depth Erasing Weak EchoesScope Display 32.3User Menu Suppressing Interference Suppressing Low Level NoiseSelecting Background and Echo Colors Alarms White Marker Fine Adjustment of Gain in Dual-Frequency OperationOptional Mode Displaying the Optional Mode MenuSystem Menu System menu 1 description System menu 2 descriptionSystem menu 3 description Bottom Level Demonstration DisplayEcho Offset TVG LevelBottom Echo Interpreting the DisplayZero Line Fish School EchoesSurface noise/aeration Surface Noise/AerationChecking Maintenance & TroubleshootingCleaning the Display Unit Transducer MaintenanceTroubleshooting TroubleshootingTest Pattern TestClear memory display Clearing the MemorySpecifications of Color LCD Sounder Power Supply Index-1 IndexIndex-2