GPSMAP 3005C Owner’s Manual usIng sonAr > sonAr tAb• Automatic Scroll Speed limit—automatically adjusts the Scroll rate withthe speed of your vessel. Entering your maximum cruising speed producesa 100% scroll rate when you reach that speed. One half of that speedproduces a 50% scroll rate, and so on. The default is 30.0 kt.• Keel Offset—allows you to offset the surface reading for the depth of akeel. This makes it possible to measure depth from the bottom of your keelinstead of from a transducer’s location near the water line. Enter a positivenumber to offset for a keel. You can also enter a negative number tocompensate for a large vessel that may draw several feet of water, requiringthe transducer to be submerged if you want to measure from the water line.The Keel Offset is reflected in the depth reading.Transducer at surface.Enter (+) a postvenumber to show depthfrom bottom of keel.Transducer at bottom of keel.Enter (-) a negatve number toshow depth from surface.• Transducer Type—allows you to specify what type of transducer you areusing, either Dual Beam or Dual Frequency.• Custom Range—allows you to specify a custom viewing range or scale.When On, this range appears as Custom in the Range setting. The leftvalue is the top of the scale and the right value is the bottom of the scale.• Calibrate Water Speed—this is available only if you are using a speed-capable transducer/sensor. Calibration is required to ensure that the WaterSpeed shown on your unit is accurate. The unit automatically uses the GPSground speed, if it is available, for comparison on the calibration. If a GPSground speed is not available, use either your boat’s speedometer reading(not always accurate) or a stopwatch to determine your speed over a certaindistance (distance / time = speed). It is recommended that the calibrationtake place in water having little or no current.To calibrate the water speed:1. On the Sonar tab, press the Cal Water Spd soft key.2. Bring the boat to a cruising speed. Both the top ground and uncalibratedwater speeds are shown at the bottom of the calibration window. Note yourtop speed, stop the boat, and press ENTER.3. By default, the top ground speed automatically appears in the “Whatwas your top water speed?” field. If a ground speed is not available,the top uncalibrated water speed is used instead. If the new speed iscorrect, highlight OK, and press ENTER. If you want to manually entera calibration, press ENTER on the speed field, enter a new speed, andpress ENTER.Graph Sub TabUse the Graph sub tab to select the color scheme, fish symbols, and scale.sonar