Garmin Fishfinder 240 Owner's Manual

Also see for Fishfinder 240 Blue: Specifications Owner's manual Owner's manual Owner's manual Pilot's guide

Contents

28On the Water28On the Water112233Understanding SonarIf you are familiar with sonar, and can determine what is on the chart,this section may not be for you. This section is intended to help the noviceuser gain some understanding of how the Fishfinder 240 operates and howit can help improve their fishing productivity.To understand what the unit is displaying, it is important to have ageneral knowledge of how the unit works and how it determines what todisplay. Briefly described, the unit operates by transmitting sound wavestoward the bottom of a lake, stream or seabed in a cone shaped pattern.When a transmitted soundwave strikes an underwater object such as thebottom, a piece of structure, or a fish, sound is reflected back to thetransducer. The transducer collects the reflected sound waves and sendsthe data to the unit to be processed and displayed on the chart. Theunderwater data is displayed on the chart in the order that it is returned:first returned—first on the chart. The diagram in the sidebar demonstratesthis showing an underwater scene as it would be displayed on the chart.Generally speaking, if the only thing between the transducer and thebottom is water, the first strong return will come from the bottom directlybelow the transducer. The first strong return sets the bottom level. Weakersecondary returns provide the detailed data. Stronger returns will displayin darker colors, black being the strongest return. In Example 2 (page 30)you can see that the branches and the fish were the strongest secondaryreturns and are indicated in black on the display.That is brief description of how your Fishfinder operates. Let’s take alook at how this data can help you to improve your fishing.Unit Operation and the ChartThis fish is currently in a Dead Zone and is not detectedby the sonar. The fish is in the coverage area of thetransducer, but remember the first strong return sets thebottom level. The fish will never be detected since thebottom level will never be set below the fish. The fish onthe right side of the display (shown in light grey) will bedetected and displayed when the transducer cone passesover the fish.