Garmin GPSMAP 238 Sounder - Manual (Page 50)

40
Reference
Sonar Page Options
Calibrate Water Speed — this is only available if you are using a speed-capable transducer/sensor.
Calibration is required to ensure that the Water Speed displayed on your unit will be accurate. The
unit will automatically use the GPS ground speed, if it is available, for comparison on the calibra-
tion. If a GPS ground speed is not available, use either your boat’s speedometer reading (not always
accurate) or a stopwatch to determine your speed over a certain distance (distance / time = speed).
It is recommended that the calibration take place in water having little or no current.
To calibrate the water speed:
1. On the Sonar tab, use the ARROW KEYPAD to highlight ‘Calibrate Water Speed’ and press
ENTER.
2. Bring the boat to a cruising speed. The top ground and uncalibrated water speeds will be shown
at the bottom of the calibration window. Note your top water speed, then stop the boat and press
ENTER.
3. By default, the top ground speed is automatically shown in the ‘What was your top water speed?’
fi eld. If a ground speed is not available, the top uncalibrated water speed is used instead. If the new
speed is correct, highlight ‘OK’ and press ENTER. If you wish to manually enter a calibration, press
ENTER on the speed fi eld, enter a new speed and press ENTER.
4. You may also press MENU from the calibration screen and choose ‘Use Top Ground Speed’ to
default back to ground speed or ‘Use No Calibration’ to use the speed sensor’s uncalibrated speed.
NOTE: If the boat is not moving fast enough or the speed sensor is not outputting a
speed, you will see a “Boat Is Not Moving Fast Enough To Calibrate” message at the
bottom of the display. Check that the speed sensor wheel is moving or safely increase
boat speed. If there is a problem with the speed sensor/unit or if a speed senor is not
installed, a “Water Speed Sensor Is Not Working” message appears at the bottom of
the display. Check connections of speed sensor cables.
• Page Defaults — restores the Sonar Page settings to the original factory setup.
To restore default settings to the Sonar Tab:
1. Press MENU. With ‘Page Defaults’ highlighted, press ENTER.
Keel Offset:
Transducer at Surface
Enter (+) positive
number to show depth
from bottom of keel
Keel Offset: Transducer
at Bottom of Keel
Enter (-) negative number to
show depth from surface
Calibrating the
Speed Sensor
,
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