Garmin GPSMAP 3005C - Marine GPS Receiver Owner's Manual

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GPSMAP 3005C Owner’s Manual 3usIng sonAr > understAndIng sonArThe wide beam is helpful in shallow water, because it gives you a much widerview of objects in the water, including areas beyond the sides of your boat. At a30-foot depth, the wide beam covers the area of approximately a 20-foot circle.Understanding the Sonar DisplayOne of the first things to understand about sonar is that the transducer sends abeam down to the bottom of the water, much like the beam of a flashlight. Thebeam starts small near your vessel and expands as it gets to the bottom.The Sonar Page does not show a 3-D representation of the underwaterenvironment. Instead, the display is in two dimensions, much like if you took apicture of an aquarium. Only the depth of the item in the water is shown.The strongest sonar returns appear on your screen as the most intense solidcolor (depending on your selected color scheme; red is the default). The weakestreturns appear as the less intense, less solid colors (blue is the default).The bottom of the water is always going to be the strongest signal, and thereforethe most intense color. The bottom is the continuous, intensely-colored linerunning across the bottom of the screen. The GPSMAP 3005C includes the latesttechnology in interpreting bottom signals; it can see through fish, structures, andthermoclines (shown in the weakest colors). However, large schools of fish ordense structures close to the bottom can affect water depth return readings.NOTE: If the GPSMAP 3005C is unable to track the bottom for any reason,the digits in the depth window flash on and off to alert you that the unit is nottracking the bottom.At the top of the screen, you might see a grouping of intense colors. This area issurface clutter, which can be caused by waves or any other sonar interference atthe surface of the water. Too much surface clutter can obscure your view of fish.You can turn down the Gain setting to reduce this surface clutter.Between the bottom and the surface clutter, the fish appear as arches. Actualfish returns might not always appear as perfect arches, due to the speed, fishorientation, or other conditions. You can turn on the Fish Symbols setting if youwant to see on-screen fish in a fish shape.Fish Symbols Turned OnThe strength of the sonar return can also help you interpret the hardness of thebottom of the water. The thicker the bottom line, the harder the bottom.Hard Structure Soft Structuresonar