Garmin GPSMAP 3210 Owner's Manual - Page 84

Using Sonar > Understanding Sonar Using Sonar This section covers the additional options for the GPSMAP 3206/3210 when used with a GSD 20, GSD 21, or GSD 22 sounder module. Read the installation instructions included with your sounder to install it. NOTE: You must have a GSD 20, GSD 21, or GSD 22 sounder module installed and connected to your GPSMAP 3206/3210 to use the sonar features. The following section provides a general overview of sonar and the things you need to know to help you use the sonar functionality of your GPSMAP 3306/3210. Understanding Sonar The transducer mounted on your vessel sends sound waves down into the water in a cone shape, similar to a flashlight beam (covering a smaller circular area at the top and angling out to a larger circular area at the bottom). These sound waves reflect off of any object that they hit, and then the waves travel back up to the transducer. These objects could be fish, branches, the bottom, or any other object that has a density that is different from the water. The transducer receives the sound wave information, and then sends the information to the GSD 20, GSD 21, or GSD 22 sounder module and then to the GPSMAP 3206/3210. The GPSMAP 3206/3210 displays the information on the screen for you to see and interpret. The type of transducer and the settings that you choose determine how the information is displayed on the screen. frequencies to get the information that you want. If you choose dual frequency, the transducer alternates between the 50 kHz and 200 kHz signals. This capability allows you to see the best picture available at any depth. Using Dual Beam Dual beam works best for shallow water (for example, inland) applications. A dual beam transducer can transmit a narrow or a wide beam. The water area covered by the transmitted sound waves is determined by the beam width of the transducer and the water depth. The narrow beam provides crisp detail of what is under your boat, and is very helpful if you are fishing in deeper water where the beam covers more area (for example, at a 30-foot depth, the narrow beam covers the area of about a 7-foot circle). Narrow Beam Wide Beam Sonar Using Dual Frequency Dual frequency works best for deep water (for example, off-shore) applications. The 200 kHz frequency allows you access to great detail about what is underneath your boat. The 50 kHz frequency provides less detailed information, but penetrates to greater depths with the same power. You can choose either or both 76 GPSMAP 3206/3210 Owner's Manual