How Do Fish Finders Work?

How Do Fish Finders Work

Fishing is a sport and hobby for several people, and it’s quite easy in fresh and clear water. But when you go fishing in muddy water it’s hardly unclear to see what type and number of fish are underneath your boat. That is when you desperately need to know about the usage of a fish finder. But the question is, how do fish finders work?

Fishfinder is used to serve several purposes as it helps in the detection of underwater life, plantation, and much other hidden information present in the depths of the water.

By the transmission of ultrasonic waves, fishfinders help us in understanding the underwater information, distribution of fish schools, water depth, and conditions of the seabed.

Fish finders transmit ultrasonic sound waves into the water, these waves then hit the objects present beneath in the water it can either be fish or any hard object. Part of these waves is reflected to the transducer of the fish finder which then projects a raw image. Hence a fishfinder works on the principle of ultrasonic reflection.

After a pulse is received by the transducer another one is sent out at that very moment.

Because sound waves can only travel as far as one mile in a second that is why fish finders produce multiple pulses in a second. Professional fish finders like the deeper PRO, Pro+, Pro+2, and Deeper CHIRP2 all send almost 15 pulses per second.

The pulses that are received back are transformed into electrical signals for interpretation. The anglers then can estimate the depth and texture or hardness of any bottom surface or objects that may be present beneath.

How Do Fish Finders Work?

A fish finder is a gadget that utilizes sonar technology and helps in the identification of fish and other objects present underwater like rocks, plantations etc.

The standard fish finders usually have a color chart display that projects the signals received by the fish finder on the screen. An experienced or professional angler can identify different icons on the screen and can explain the location and type of fish.

The ultrasonic waves from the fish finders are directly transmitted beneath the boat. If the pulses or waves happen to hit a fish school, very little or too weak reflections will return back to the transducer (from where the pulses were sent).

How Do Fish Finders Work

The returned signals or pulses are converted into electrical signals and are ultimately sent to the receiving circuit of the fish finder. The circuit is used to amplify the weaker signals, and then they are passed to the processor for further processing.

It then generates user-friendly images that are then displayed on the screen. The image is represented on an LCD. Strong reflections are usually represented in red and yellow colors, whereas weaker reflections project themselves in blue and green colors on the screen.

Fishes having high-density and heavy rocks on the seabed return as stronger reflections, so they usually project in red color. On the other hand, low-density objects and fish will be shown in blue color. The representation of colors in the reflected image will show you the ultimate picture underneath.

Fish Finder Components:

A typical fish finder consists of the following components:

  • Main unit
  • Transducer

The main unit is usually easy to access, and it should be located where it is easy to locate and that is why it is present mostly in the cabin or the wheelhouse, etc. On the other hand, the transducer is placed on the bottom of the boat via hull or in-hull installation.

You should keep one fact in mind, that the efficiency of a fish finder depends on its proper installation on the boat’s bottom. If the transducer is not planted properly it will not capture the reflected images properly and may result in some other serious defects. That is why before actual installation you must communicate with a professional to properly install the transducer.

Does A Fish Finder Help?

Fish finders are extremely helpful tools in fish and the detection of other objects that are present beneath the water. With this tool, you can detect any fish and its structure you may not even know were there. However, fish finders take time and require experience and knowledge. Any mishap during the buying process can greatly affect the performance, and may not be able to show you the complete or high-quality image.

What Does A Fish Finder Do?

A fish finder also known as a sounder is an instrument or tool used to detect fish, plantation, and any other hard objects that are present in the ocean or sea.

It uses sound waves or impulses for locating the fish, the reflected pulses are translated to know how big a fish is or where it is.

Using sound pulses SONAR or fish finder detects the object or fish presence.

Unlike light waves, sound waves do not travel in straight lines. Instead, they scatter in the form of cones and get wider with the distance.

In most fish finders, one can adjust the frequency of the sound beam to control the range of the sound wave cone. It is important to adjust the range because at different locations and for different fish species you have to adjust accordingly.

Wide beam scanning which usually ranges from 40 to 60 degrees is great if you want to have a quick look or scan of the wide areas. It provides you a general and an overall estimation of the general depth and bottom structure.

However, in this case, the efficiency and accuracy would be lower. It explains that if you are scanning at the depth of 45 ft you can see the objects within an area having a diameter of 47ft / 14,3 m.

On the other hand, narrow beaming which usually ranges from 20 degrees to 80 degrees gives you a more precise image and has greater accuracy. However, with a small angle, you cannot cover a huge area. When you want to locate the exact position of the fish then narrow beaming is excellent. It is also more suitable for deeper water because its cone does not get wider in the water.

How Deep Does A Fish Finder Work?

The standard depth range with these broadband devices is 10k feet, which includes all the major brands that produce sounders or sonars. Some of the fish finders come with a specific feature called the ” dual transducer option”, which allows you to simultaneously and independently send pulses of sound waves in the water. That means you can entirely customize your sounder or fish finder because you can change the range and frequency of the transducer.

How Deep Does A Fish Finder Work

Most of the fish finders can transmit sound waves of both high and low frequencies simultaneously.

The waves of low frequency provide a better view and penetrate deeply into the water. It also requires a low amount of power to generate and also does not produce much sound.

Ultimately it causes a ” whisper in the ocean” which allows us to detect fish without alarming them. The higher frequency beams are good for mid-depth waters and shallow waters for bigger objects.

Related Articles:

How Does A Sonar Work?

How to install a fishfinder?

How Do They Separate Fish From Turtles?

Fish and turtles are two different creatures, they are anatomically different and they also have different moving patterns. Fishes wriggle in the water in a very specific movement that is very different from the turtles.

That is why there are a lot of differentiating points for the finder to distinguish between the two. Finders also see the texture of the creatures to detect and locate them. In some sounders or finders, they practically touch the object to differentiate if it’s a fish or some other creature.

Turtles are very scaly and hard as compared to fish, while fishes are very slimy and soft. As fish finders work on the Sonar technology which sends echo or sound waves and the water and then translates the reflected images.

The images are translated via a trained inspector which is capable of differentiating among the signatures of different species.

In the case of fishes and turtles, they both return an echo signature for the translation to interpret but they won’t be the same. But a professional can easily determine even the minor difference between the two signatures though they look the same. However, there are some cases when the returned echo signatures are exactly the same but you can differentiate among species and creatures depending upon their movements and patterns.

How Do Fish Finders Detect Fish?

Fishfinders are great for fish detection but how do they do it? They normally detect the air present in the swim bladders of the fish which has a different density than the water.

The air that fishes store in their swim bladders reflects the sound waves back to the transducer. The fish finder then translates these reflected sound waves into raw images that are ultimately processed by the fish ID into user-friendly images.

Most of the fish finders operate on low and high-energy beams that scatter into the water in the shape of a cone. Fishes that happen to swim within the radius of this cone will reflect back the sound waves to the transducer and the finder will capture them in the form of an image on the screen.

A group or school of fish will be represented as different shapes and figures in the image. It depends on how large the group or school of the fish is, it also depends on how many fishes are within the cone. Individual fishes that are normally present in the deeper water also reflect back the waves, but they may appear in the form of arches.

As the fish moves from the sonar beam the reflected forms and arch. The mark begins to appear on the screen when the fish enters the outer edge of the cone.

As soon as the fish moves further in the cone, ultimately the distance between the fish and transducer is reduced, so the mark starts to acquire a shape or arch due to bending.

When the fish is at the center of the cone that means it is directly under the transducer. As a result, the mark starts to get flat as the fish moves closer to the transducer.

As fish moves to the outer edge of the cone, that means it is moving away from the transducer. Hence the mark begins to bend downwards as the distance between the fish and the transducer increases. As a result, you see an arch on the screen chart of the display showing the distance and the movement of the fish on the screen.

How Do Portable Fish Finders Work?

Like all other fish finders, portable ones also work on the SONAR technology. The transducer is the most essential component of a fish finder that emits sound waves. If there is any object or fish present in the path of the beam, the objects will reflect back these waves in the form of impulses to the transducer.

After that, the gadget’s AI or software will calculate the distance and the location of the object/fish. It calculates the distance by calculating the seconds the waves took to get, hit, and come back.

The most fun part is that you don’t have to do any of the hard parts, like calculating the fish finders. You can view every information on the screen, from there you can have an estimate about the depth and the location, based upon those readings. With such information, you can estimate whether either point is good for fishing or not.

How Does A Fish Finder Work Effectively?

A fish finder will work effectively only when you know how to operate it. For that, you must be aware of the necessary steps you need to effectively operate it.

  1. You have to turn on the power unit.
  2. Quickly read the individual user unit interface.
  3. Adjust the most suitable setting according to your need, or set the finder to default or auto mode.
  4. Learn how to interpret what you see on the chart or screen of the finder.
  5. Catch the fish.

If you are a beginner you would probably end up with a traditional fish finder that uses low-frequency beams to give you a general image of what’s beneath the water.

With such finders/sounders, the sonar sends a bunch of beams every now and then and records what reflects back, then the reflected beams are translated into data and then into the image.

As multiple beams reflect back from multiple waves data begins to accumulate on the screen from left to right providing you a proper picture.

Anything or object that causes the wave to bounce back to the finder is most probably a fish. Such fish finders can be hard to use when the boat is moving at a slow rate or is static.

However, they work best when the boat is moving at a constant steady rate, then you can have a proper estimation of the depth, features, and the type of the sea bottom or sea bed.

If you observe thick lines on the screen that means the bottom is softer. On the other hand, thin lines mostly represent hard surfaces, hard bottoms like rocks, gravel, etc.

If you want to effectively use a fishfinder remember that the chart always moves from left to right. The chart is not based on the boat’s movement but works on the time scale.

In case the boat is still the chart will constantly scan and will keep moving from left to right. It means that sonar is scanning the same location repeatedly from time to time. In such cases, the anglers get confused about what is displayed on the screen.


Fish finders are extremely beneficial when it comes to the detection of the fish, estimation of the location, finding sea depth, and for several other purposes. As the technology is developing one can use different types of sonars depending upon their location and fish species. There are also now user-friendly sonars that help in easy detection, and they also create user-friendly images that are easy to interpret and work with.

Ricki Cooper

I have been fishing for 11 years. I believe in the famous saying "If fishing is interfering with your business, give up your business".

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