NorthStar Navigation EXPLORER 657 operation manual Shadows, Example of shadows, When to use 50 kHz

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Shadows

Shadows are created around areas where the ultrasonic beam cannot ‘see’. These areas include hollows on the bottom or beside rocks and ledges, where the strong echoes returned off the rocks obscure the weak echoes of the fish and may also create a double bottom trace. See following for an example of the sonar display in such an environment. A double bottom trace is shown on the display.

When looking for fish with the wide angled 50 kHz frequency, be aware of increased shadows. Use the high frequency 200 kHz in areas that have rocks and ledges because this frequency reduces the shadow effect considerably.

Example of shadows

Sonar display of same area

A

B

AFish is visible on the display

B Fish is hidden by the strong echoes off the bottom and is not

A

B

A

A

shown on the display

8-3 Single and Dual frequency fishfinding

Sonar frequencies

discrimination capability and is particularly good

The 657 has two sonar frequencies, 200 kHz and

at showing individual fish, including bottom

dwellers.

50 kHz. To select the sonar frequency to use:

 

1 Go to a sonar display (see section 9).

When to use 50 kHz

2 Press

, select Frequency and select

The 50 kHz frequency is particularly suitable for

use in deep water, typically greater than 500 ft

200 kHz, 50 kHz,or Mixed.

(150 m).

When to use 200 kHz

At 50 kHz, the cone covers an area of water about

The 200 kHz frequency is especially suitable for

four times wider than the 200 kHz cone and

use in shallow and medium depth water, typically

penetrates to a greater depth with minimal loss of

less than 500 ft (150 m) and while running at

the return signal.

speed.

 

 

However, it produces a lower definition display

At 200 kHz, the narrow cone reduces any noise

with more shadow compared to the 200 kHz

caused by air bubbles.

frequency. This means that a group of small fish,

 

 

The 200 kHz frequency generates a higher

for example, could be displayed as a single item,

definition pulse which produces little shadow

while any fish very close to the bottom may not

and returns excellent detail over a small area

be found at all.

of bottom. Therefore, it gives excellent bottom

 

34

Northstar Explorer 657 Installation and Operation Manual

Image 34
Contents Explorer Could result in minor or moderate injury Possible injury or deathCould result in death or serious injury DamagePage Contents Tides window User card window 15 AIS Installation Northstar petrol/gasoline sensors Installation Other Nmea instrumentsIntroduction Plug-in cards Cleaning and maintenanceOverview 657 can use two kinds of plug-in cardTurn the display unit off see -2 and put the dust cover on Changing the plug-in cardRemoving the display unit Replacing the display unitBasic Operation Using the keysUsing the menus Overview of the keysTurning on and off / auto power Turning on manually Turning off manuallyTo cancel MOB or set another MOB Backlight and night modeNight mode Man overboard MOBSimulate mode Alarms657 has user settable alarms see section Main windows Page Multi window displays Adding a favorite display to the list Favorite displaysSelecting a favorite display Deleting a favorite display from the listCompass Setting the data header for a displayData header Displays can show data at the top, called the data headerIntroduction to navigating Navigation ChartGoing to a waypoint or to a point on the chart Navigating to a pointPreparing Starting a route from the chart windowCancelling a route Starting a route from the routes windowTypical chart window shows Chart windowTo go to the Chart window, press then select Chart Land Sea Cursor see section Typical waypoint see sectionChart symbols and information Chart modesChart scale Latitude and longitudeDistance and bearing calculator Finding a chart symbolPerspective view Projected courseTime intervals Interval Track Track 2, 3, 4 or Navigation Highway windowTracks and tracking Interval Track Track 2, 3, 4 orNavigation Waypoints Waypoints windowCreating a new waypoint Displaying a waypoint on the chartManaging waypoints Moving a waypointChanging a waypoint’s data Navigation RoutesDeleting all waypoints Sort WaypointsManaging routes Creating a new route from the chart windowRoutes window Creating a new routeEditing a route Displaying a route on the chartEditing a route from the chart Creating a new route from the routes windowSatellites Satellite window UsingSonar fishfinding Introduction Satellite window showsInterpreting the display Strength of echoesWater Bottom typesFrequency and cone width DepthShadows When to use 50 kHzWhen to use 200 kHz Example of shadowsWhen to use Mixed When to use 50/200 kHzKHz display 200/50 Khz display Mixed display Minute ago Seconds ago NowFish symbols Fish detection and display Where to find fishFish arches Auto Range657 has two range modes Zoom range and offsetGain window Changing modeGain and threshold This display is called the gain windowSonar fishfinding Displays Sonar history display no splitScreen. Press to return to the most recent echo Extended history modeSonar Zoom and Full Screen Zoom displays History position barSonar Bottom display Sonar 50/200 displayFish recognition Setting gain and thresholdSonar A-Scope display Bottom typeSelecting a Gauges layout Gauges windowData window Changing a gauge layoutFuel window Fuel functions and displayWhat the fuel computer does Fuel window showsWhen you add or remove fuel When you remove fuel Low fuel alarmBoat speed sensors Speed Log Economy Range Water speed and ground speedSpeed Log Economy Start running the boat in a straight line Fuel consumption curvesMaking a curve Press twice, then select FuelDeleting a curve Using a curveRenaming a curve Selecting a curveCalibration Setup enginesTo the reading of the fuel dispenser’s gauge Then press Tides window Choosing the date of the tide chartTides window shows data for the chosen date User card window has User card windowSaving data to the user card Sorting the file names 15 AISDeleting a file from the user card Rereading the file informationViewing AIS Vessels Vessels Safety msgs rxAIS Windows Displaying Full AIS Details16 DSC/Buddy track windows Displays Distress PollCreating a waypoint Using the displays Displaying a boat on the chartBoat positions Deleting a boatSetting up SmartCraft Setup option menusTime see Favorites see 17-14 Simulate see Factory reset Setup SystemAuto power off LanguageRotation Setup ChartSetting map datum PaletteApplying a map shift Nmea datum offsetMap shift Map shiftLat/lon grid Frequency Setup SonarPulse power Digit sizeGPS Source Setup GPSSetup Fuel Dgps SourceSource Setup enginesSetup tanks Num enginesTime Setup TrackDistance RecordReset total dist Setup AIS Show Dangerous OnlySetup Logs Reset engine hoursArrival radius Anchor alarm Setup AlarmsSymbol Alarm Alarm sounds when it is onSetup Comms Setup UnitsTemperature FuelSpeed Setup CalibrateTemperature filter Speed filterKeel Offset Setup TimeSetup Favorites Speed rangeSimulate InstallationSetup Simulate ModeOptional sensors and instruments Installation What comes withInstallation Options and Accessories GPS or Dgps antenna For GPS navigation see sectionConnections Power/data cablePin Wire Function Display unit 18-3 Black Yellow BlueBracket Mounting Installation The display unitFlush Mounting There are two mounting arrangementsBlack Power/data cable Red Yellow Fuse 2A Installation Power/data cableBasic power Auto powerInstalling an antenna Installation GPS antenna Selecting an antennaDgps Source Installation Northstar petrol/gasoline sensors Installation Sonar transducerBlue Sonar cable Either Installation Other NavBus instruments Installation SmartCraftNavBus Installation Northstar VHF radio Installation Other Nmea instrumentsIf the display unit is bracket mounted, adjust Installation Setup and testEnter setup data to set up the 657 to your Tilt and rotation for best viewing and handAppendix a Specifications Adindan Afgooye List of datumsSouth American Appendix B Troubleshooting General problemsGPS navigation problems Fuel consumption problemsErratic Fuel Flow readings Sonar fishfinding problemsTwin engine installation shows only one flow rate There is no reading for fuel economyBottom is displayed too far up the screen Bottom is not displayedThere is a double bottom trace displayed Appendix C Glossary and navigation data GlossaryNavigation data TBMFT!COUNBSJOFDPN