Home Fishing How Does a Fish Finder Work?

How Does a Fish Finder Work?

How does a Fish Finder work

Although many anglers are aware of fish finders, very few actually know how to use them to catch fish. So, how does a fish finder work? Keep reading to see what fish finders do and how they operate.

What is a Fish Finder?

In addition to detecting the presence of fish and water depth, fish finders also provide information on other underwater objects. They can show things like rocks and wreckage or even schools of fish that our eyes are unable to observe.

Excessive competition in the market is driving innovation in the technology of fish finders. Therefore, it’s recommended that you keep an eye on the market to ensure you don’t overpay for a technology that may be redundant soon.

Types of Fish finders:

  • GPS Combo Device
  • Castable Fish Finder
  • Chirp Fish Finder
  • Chartplotter
  • Standalone Sonar Unit
  • Portable Fish Finder
  • Smartphone Fish Finder
  • Fully Network System Device

Despite having different features such as color, screen size, pixel, frequency and power, fish finders primarily do the same job to provide the angler with a graphical understanding of the composition underneath the surface of the water.

How Does a Fish Finder Work?

Two Basic Parts of Fish Finder: Fish finders consist of two main parts, a transducer, and display. These two units are correlated with a transmitter and receiver.

The transducer acts as the ears of your fish finder. The display operates as your third eye to locate fish beneath the surface of the water.


The transducer can be attached in a couple of different places. Either placed on the outside of the boat through the hull or on the trolling motor mounted in the water.

The transducer operates similarly to sonar technology by recognizing objects in the water by using electrical signals. It then displays the size and distance of these signals on the display unit through art-like graphics.

The Function of the Transducer Under Boat

The electrical wave generated from the transducer is passed to the transmitter through the water. It is only when this electrical wave is interrupted by an object in the water that it will generate a display on the unit.Information on the shape, size and altitude of the object is then communicated to the display unit.

However, the precision of the information on the length and weight of the object in question will depend on the power and frequency of your fish finder.

The fish finder can calculate the distance of the object from the transducer by accounting for the time interval between the transmitted wave and when the signal is received by the display.A useful fact to know is that the constant speed of seawater wave is determined as 1500 meters per second and whereas freshwaters are 1463 meter per second in freshwater.


The display is definitely the most important part of the device because it is the mechanism through which information is conveyed to the angler.

Displays show all the necessary information including the location of fish, water depth, temperature, bottom shape, speed over water, and types of fish. Ultimately it is down to human interpretation as to how useful a fish finder will be. The angler will have full control of how they wish their display to function.

Basic Function of a Display

An example of a display feature which the angler will manipulate is the sensitivity setting. Through synthesizing sensitivity of the unit, the power of the fish finder will become adjustable.

With a reduced power of sensitivity, the image on display becomes less reliable to interpret. The best displays have a strong color resolution to enhance the quality of the images displayed.

How Are Fish Detected using a Fish Finder?

When a fish has been detected, there will normally be an arch-like shape on the display of your fish finder. Using the fish ID landmark technology, the majority of fish finders will be able to differentiate fish from other objects including vegetation and rocks.

This is possible because the space between the fish and the transducer is altered when the fish swims compared to other objects which are not movable.

Are There Differences in Quality Between Price Ranges for Fish Finders?

Basic fish finder models will only give rough estimates on locations of fish, whereas intermediate models provide more accurate estimates and can update quicker as you move along the water.

Advanced models are very accurate and will be able to tell the difference between types of fish in the water. Therefore, if you are after a specific catch, advanced technology on more expensive fish finders will assist you in giving accurate information to assist your fishing experience.

Most intermediate and advanced models should also include a GPS capability, which can be very handy because if you discover a particularly fruitful location, the fish finder can save your GPS coordinates to ensure easy access to the sweet spot in the future.

Do Ice Fish Finders Work Differently?

Ice fishing flasher is different from other types of fish finders. Although they also use a sonar pulse, this pulse is sent down to the bottom of the water and then bounces back to the surface.

It will display a signal if the pulse hits an object when returning to the water surface, recording the depth and intensity of the object in question.


Reading a fish finder should quite a straightforward process. Depending on the quality of the model, you will receive either rough estimates or accurate information of the presence of fish beneath the surface of the water.

It is important that you consider fish finders as a guide and not a guarantee. You still need to be competent in using your rod and lure to catch the fish. The fish finder will, however, recommend potential areas for high yields.

Hopefully, this article answer the question how does a fish finder work. Just remember, before purchasing model, you should identify a budget. There maybe try a cheaper version that works just as well! If you have any questions, ask away in the comments!


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