Fish Finder Sonar (2024 Beginners Guide)

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It’s all well and good owning a fishfinder but if you don’t know how fish finders actually work, then you’re not going to get the most out of them you might be wasting some precious time trying to figure out how they work when you’re fishing. 

Fish finders come with all kinds of features that can be mind-boggling to understand. I used to just turn on my fishfinder and go fishing, but then I did some research into how they work, and afterward I could change the settings depending on the site I went to and find fish more easily. 

Join me as we take a look at how a fishfinder works with sonar so you can get the most of your model.

Do fish finders use sonar? 

Fishfinders on a Table
Fishfinders on a Table

Yes, in order to find fish, every fishfinder uses sonar technology for mapping what is under your boat picking details such as fish, depth contours, structures like fallen trees, and other details like debris, rocks and seaweed. 

What is fish finder sonar?

Fish finder sonar is like any other sonar, which means it sends pulses of energy with a specific range into the water to show you what is beneath you. 

What is the difference between a fish finder and sonar?

Sonar is a way of detecting or mapping what is around you in the water or even in the air using sound waves. It’s used, for example, by animals such as bats and whales so they don’t swim or fly into objects, and to locate any sign of food sources. It can also be described as a kind of echolocation

A fishfinder is a device that features sonar technology inside it which is then used by fishermen for mapping areas to see structures and features under the water so they can find fish and catch more. 

How does sonar work on a fishfinder? 

A fishfinder comes in two parts: a display/screen and a transducer. The fish finder transducer is put into the water and is connected via cables to the display/screen on your boat. 

The transducer then sends out sound waves into the water and collects the reflections of the waves when they return. The reflections are created when the waves bounce back off anything in the water, such as fish, the bottom, underwater structure, rocks and more. 

Deeper Fishfinder Sonar Scanning
Deeper Fishfinder Sonar Scanning

All the reflection data is then sent to the display unit, which then calculates the data of the reflections, and at the same time, turns them into an image you can read of what is in the water for you to see on the display. 

If you’re getting incorrect readings, you might be having issues with your transducer. This guide about knowing if the transducer is bad might help.

How can you tell which direction the sonar is going on the fishfinder? 

This depends on the fishfinder model and the ability it has. 99% of the time, your fishfinder will be pointing at the bottom of the water, and so the direction it’s going in will be the direction our boat is moving. 


Remember a fishfinder scans what is underneath it, so if it’s moving, it’s always scanning in the direction it’s moving in. 

How to set up a fish finder sonar?

How to set up a fishfinder depends on the model you have. Generally, on a boat, you will need to install the screen on the center console and have the transducer mounted on the bottom of the boat, with cables running to connect the two. Then you need to wire them to your boat battery. 

Once on and working, you can change the sonar settings in terms of the wave frequency you desire, and the ping speed you want the waves to go out at. The hard part is picking the right settings for the areas you’re fishing in. 

What is ping speed?

Ping speed describes how often your transducer sends out a burst of sound waves into the water. 

You don’t want it pinging all the time, as your display unit will end up showing you too many details, and overlapping ones too, on the screen making it hard to find and catch fish. 

If the ping speed is too slow, you’re going to miss out on areas between the pings, and you want to match it with how fast your boat moves. 


Slower ping speeds will show you a better bigger picture of the bottom features. 

How to set up sonar fishfinder ping speed

The ping speed, also referred to as scroll speed, can be changed easily from the display. Go into settings and find the scroll or ping speed, and start the day with it at its lowest to see what data it will provide. They play with it throughout the day to see how the image changes and what you can read on it. 


If you increase your speed, increase your ping speed a bit to match so you don’t miss out on areas that might be good for fishing. 

What is sonar only on a fishfinder? 

If you own a sonar-only fishfinder, it means you have a model with only a sonar ability for mapping fishing areas. Other fishfinder models can come with both a chartplotter and GPS in one single unit. 

If you opt for a fishfinder model that includes a chartplotter and GPS, your ability to find fish, catch more, and increase your fishing success goes through the roof, and here is why. 

The chartplotter feature allows you to add lake maps and sea maps (charts) which show you the underwater depth contours and other details like hazards and more. 

Fishfinder Mounted on a Boat
Fishfinder Mounted on a Boat

Let’s say for example you have lake maps on your fish finder and you’re searching for bass. You’ll be able to see all the drop-offs on the charts, hazards to avoid, depth changes and structures that will hold fish, and more. 

Now let’s add GPS to the charts or maps. You can now see your routes, save them, follow past routes where you caught fish or routes to get back to the dock, mark waypoints where you caught fish, save your waypoints for another trip so you can return and find them again, and more. 

The ability to see where you are in real-time with the GPS system, mark good fishing waypoints, save your mark for another day, and even mark things like hazards to avoid will provide you with all the data you could ever want on your screen to catch more fish than ever


I highly recommend getting a fishfinder with GPS and charts. 

What Are The Sonar Types? 

As you might have guessed, there are a few different types of sonar technology that you can find in a fishfinder, and the differences mostly come down to the wave frequency used in the sonar. 

Low-frequency waves go deeper into the water but pick up less detail. High-frequency waves pick up a lot of detail but don’t have the energy to go as deep as low-frequency waves. 


Understanding this is the key to understanding the types of sonar, whether you need them, and when to use them. 

What is CHIRP sonar?

CHIRP sonar sends out a mixture of both low, medium, and high-frequency waves giving you the most comprehensive image on our screen/display. 

The low-frequency waves go to the bottom while the medium and high-frequency waves pick up all the little details so you can see every fish in the entire water column. 

Here’s a video from Garmin explaining how CHIRP sonar technology works…

Garmin Sonar Technology

What is downscan sonar? 

Downscan sonar uses two wave frequencies, usually high and low, to scan under the boat and thus create a solid image on the display of the fish, bottom, and structure. It’s not as good as CHIRP but it still finds fish. 

What is imaging sonar?

Imaging sonar is another name for the sonar you get in a fish finder. It sends out sound waves to create an image on your display of, for example, fish and other things. The image is full of different colors which is designed to make it easy to read. 

What is 2d sonar?

2D sonar is designed for lower wave frequencies and for use in deeper water. It will give you a less detailed image of what’s beneath the boat but a good indication of any fish near the bottom on your display. 

What is 3d sonar?

3D sonar creates a 3D image of what is underwater on your display. It uses multiple beams and multiple wave frequencies to create a 3D image of the site you are fishing on at the time. You’ll be able to see individual fish and even their size. 

Which types of sonar do you need and when to use them? 

The most important type of sonar to have in a fishfinder is CHIRP. If you have CHIRP then you have Downscan, Imaging, and 2D all rolled into one. You should use CHIRP all the time when trolling, drifting, or on anchor as it’ll show you everything you need to see. 

…3D option is useful if you want to spend time fishing a structure like a wreck or fallen tree.

Having a 3D option is useful if you want to spend time fishing a structure like a wreck or fallen tree. I have never used 3D as it’s expensive and not a great value to have in a fishfinder, and with CHIRP you’ll still see the wreck in real-time, and when you drop a line down you’ll catch a fish. 

Sounding Out 

Thanks for taking the time to read my article. I hope you enjoyed it and now understand how fish finders work so you can use them more effectively. If you want to learn more about fishfinders, my article about fish finder fish arches might help.

Please share it around with any of your fishing friends who would benefit from it too, and have a look at some of my best fishfinder articles so you can buy the best one of great value for your needs. 

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