Garmin Fishfinder 250 Owner's Manual

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Garmin Fishfinder 250 Owner's Manual Manual pdf 35 page image

BASIC OPERATION > U NDERSTANDING SONARFishfinder 250/250C Owner’s Manual 31Understanding SonarIf you are unfamiliar with basic sonar or need help determining whatappears on the graph, this section may benefit you. This sectionis intended to teach the novice user how the Fishfinder 250/250Coperates and how it can help improve fishing productivity.To understand what the unit is displaying, it is important to havea general knowledge of how the unit works and how it determineswhat to display. Basically, the unit operates by transmittingsound waves toward the bottom of a lake, stream, or seabed in acone-shaped pattern. When a transmitted soundwave strikes anunderwater object such as the bottom, a piece of structure, or a fish,sound is reflected back to the transducer. The transducer collects thereflected sound waves and sends the data to the unit to be processedand displayed on the graph. The underwater data is displayed on thegraph in the order it is returned (first returned = first on the graph).Generally speaking, if the only thing between the transducer and thebottom is water, the first strong return will come from the bottomdirectly below the transducer. The first strong return sets the bottomlevel. Weaker secondary returns provide the detailed data.The Fishfinder 250 displays sonar returns as shades of gray; strongerreturns are darker, and weaker returns are lighter. On the Fishfinder250C, sonar returns appear as red (strongest), orange (strong),yellow (medium), green (weaker), and blue (weakest).The diagram below shows an underwater scene as it would appearon the graph.112233The fish in the diagram is currently in a dead zone and is notdetected by the sonar. The fish is in the coverage area of thetransducer, but the first strong return set the bottom level above thefish. The first strong return to reset the bottom level below the fishwill enable the fish to be detected.The following pages will show how this data can help you improveyour fishing.