On the Water

Unit Operation and the Chart

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This fish is currently in a Dead Zone and is not detected by the sonar. The fish is in the coverage area of the transducer, but remember the first strong return sets the bottom level. The fish will never be detected since the bottom level will never be set below the fish. The fish on the right side of the display (shown in light grey) will be detected and displayed when the transducer cone passes over the fish.

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Understanding Sonar

If 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 novice user gain some understanding of how the Fishfinder 240 operates and how it can help improve their fishing productivity.

To understand what the unit is displaying, it is important to have a general knowledge of how the unit works and how it determines what to display. Briefly described, the unit operates by transmitting sound waves toward the bottom of a lake, stream or seabed in a cone shaped pattern. When a transmitted soundwave strikes an underwater object such as the bottom, a piece of structure, or a fish, sound is reflected back to the transducer. The transducer collects the reflected sound waves and sends the data to the unit to be processed and displayed on the chart. The underwater data is displayed on the chart in the order that it is returned: first returned—first on the chart. The diagram in the sidebar demonstrates this showing an underwater scene as it would be displayed on the chart. Generally speaking, if the only thing between the transducer and the bottom is water, the first strong return will come from the bottom directly below the transducer. The first strong return sets the bottom level. Weaker secondary returns provide the detailed data. Stronger returns will display in darker colors, black being the strongest return. In Example 2 (page 30) you can see that the branches and the fish were the strongest secondary returns and are indicated in black on the display.

That is brief description of how your Fishfinder operates. Let’s take a look at how this data can help you to improve your fishing.