Fish Finders Work Hard to Locate and Put You on Top of a Big Catch

Fish finders are the best tool to use so you can find and place your boat on top of the fish. All fish finders use sonar to scan the water. A sound wave is sent from the fish finder through the water forming a cone. When an object is detected, the fish finder measures the amount of time between when the sound wave was sent and when it bounced back to the unit and is displayed on the screen.

If the sound wave does not detect anything it hits the bottom. Soft bottoms such as mud will absorb the signal while hard bottoms like rock will reflect a stronger signal and send it back. The small differences in reflections are displayed on the screen and this shows how the bottom is read.

Cone angles are the measurement of the sonar beams in degrees. They are measured at "-10db" which is a way the measurement is consistent from one transducer to another and to accurately represent the capability of the fish finder. Each manufacturer and fish finder model have different cone angles. Humminbird uses an advanced multi-beam system that sends 2, 3 or even 6 sonar beams while most of the other brands use 1 sonar beam.

Here is a quick reference chart for the covered area for a specific cone angle. Example: If you are fishing at a 10 foot depth and a cone angle of 20 degrees, the area on the bottom is 3.5 feet.

20 degrees
-0.35 or roughly 1/3 of depth 24 degrees
-0.42 or roughly 2/5 of depth 30 degrees
-0.53 or roughly 1/2 of depth 40 degrees
-0.72 or roughly 3/4 of depth 50 degrees
-0.93 or roughly 9/10 of depth 60 degrees
-1.15 x depth 70 degrees
-1.4 x depth 73 degrees
-1.48 x depth 80 degrees
-1.68 x depth 90 degrees
-2 x depth 100 degrees
-2.38 x depth 110 degrees
-2.85 x depth

Fish targets will be displayed as a Fish ID symbol or an "arch" which is an unprocessed sonar return, the choice will be yours. Fish ID symbols are determined from a suspended shape being analyzed from the sonar beam to see if it is a fish. If a fish is detected, it is seen on your display as a fish graphic. Arches are displayed from the characteristics of the sonar. Fish that pass through the beam are seen as an arch on the screen. The sensitivity setting of the unit, depth of water, boat speed and location of fish will determine the size of the arch.

Clarity of the water, strong winds or currents can create air pockets and has a lot to do with the integrity of the signal. Small mineral particles such as algae, plankton or other microorganisms can absorb the sound wave instead of reflecting it back to the unit. The action of the waves will also determine the amount of air in the equation and affect the reading.

Transducers are mounted in the water on the inside of the hull, on the transom or on the trolling motor. From a cable connected from the transducer to the fish finder, an electrical signal is taken from the transmitter and turns it into sonar. The transducer should always be mounted straight down and away from motors or any other obstructions.

There are two different types of display screens available. An LCD screen is measured in pixels which shows the sonar information. The more pixels there are the clarity of the image will be better. FSTN displays provide a high contrast image for easy reading that can be seen from anywhere on the boat. They use gray scale technology that offers more detail by showing the sonar image in different shade of gray which can easily distinguish what the bottom is and what the fish are.

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