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

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Contents

GPSMAP 3005C Owner’s ManualusIng sonAr > understAndIng sonArusInG sonarThis section covers the additional options for the GPSMAP 3005C when usedwith a GSD 20, GSD 21 or GSD 22 Sounder Module. Read the installationinstructions included with your Garmin Sounder Module to install it.NOTE: You must have a GSD 20, GSD 21, or GSD 22 Sounder Moduleinstalled and connected to your GPSMAP 3005C to use the sonar features.Understanding SonarThe transducer mounted on your vessel sends sound waves down into the waterin a cone shape, similar to a flashlight beam (covering a smaller circular area atthe top and angling out to a larger circular area at the bottom). These sound wavesreflect off of any object that they hit, and then the waves travel back up to thetransducer. These objects could be fish, branches, the bottom, or any other objectthat has density that is different from the water. The transducer receives the soundwave information, and then sends the information to the GSD 20, GSD 21, orGSD 22 sounder module and then to the GPSMAP 3005C. TheGPSMAP 3005C displays the information on the screen for you to see andinterpret. The type of transducer and the settings that you choose determine howthe information is displayed on the screen.Using Dual FrequencyDual frequency works best for deep water (for example, off-shore) applications.The 200 kHz frequency allows you access to great detail about what is underneathyour boat. The 50 kHz frequency provides less detailed information, butpenetrates to greater depths with the same power. You can choose either or bothfrequencies to get the information that you want. If you choose dual frequency,the transducer alternates between the 50 kHz and 200 kHz signals. This capabilityallows you to see the best picture available at any depth.Using Dual BeamDual beam works best for shallow water (inland) applications. A dual beamtransducer can transmit a narrow or a wide beam. The water area covered by thetransmitted sound waves is determined by the beam width of the transducer andthe water depth. The narrow beam provides crisp detail of what is under yourboat, and is very helpful if you are fishing in deeper water where the beam coversmore area (for example, at a 30-foot depth, the narrow beam covers the area ofabout a 7-foot circle).WdeBeamNarrowBeamsonar