Understanding Sonar
If you are unfamiliar with basic sonar, or need help determining what is displayed on the graph, this
section may be for you. This section is intended to help the novice user gain some understanding of how the Fishfinder 250/250C 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. Basically, 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 graph. The underwater data is displayed on the graph in the order that it is returned: first returned—first on the graph. The diagram below demonstrates this by showing an underwater scene as it would be displayed on the graph. 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. The Fishfinder 250 displays sonar returns as shades of gray; stronger returns are darker, and weaker returns are lighter. On the Fishfinder 250C, sonar returns are displayed as red (strongest), then orange (strong), yellow (medium), green (weaker) and blue (weakest).
The following pages will show how this data can help you to improve your fishing.
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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 eventually be detected when the first strong return sets the bottom level below the fish.
