Informational Guide

How Does A Fish Finder Work?

Find out everything you need to know about how fish finders work. No matter the brand, our guide will help you understand and find more fish.

by Andrew

Informational Guide

How Does A Fish Finder Work?

Find out everything you need to know about how fish finders work. No matter the brand, our guide will help you understand and find more fish.

by Andrew

by Andrew

If you’re a fishing enthusiast who likes to spend their time on the water efficiently, you're probably already aware of fishfinders.

No matter the brand or model, our detailed guide will help you understand how your fish finder works and how to get the most of it.

We've got a ton of reviews to find you the right fish finder, but first, let's look at how they work before choosing the model you want.

If you’re trying to spot schools of fish in deep bodies of water, you’ll definitely need the help of a fishfinder. You’ll see a graphic image displayed on either the device’s screen or directly on your smartphone through a castable fish finder.

These devices work on the technology of the SONAR (Sound Navigation and Ranging) system. Some manufacturers use systems like GPS, electronic compasses, and radar, making the device even more reliable than ever before. These technologies work and display their findings through the transducer and the main unit.


The transducer is the heart of the echo transmitter and will display this to the main unit. A good fishfinder relies heavily on how the transducer sends and receives signals. It needs to be fully submerged underwater to get a reliable reading, so mounting your transducer will be essential.

Main Unit

The main unit will be a device that you’ll read each signal from. It usually consists of an LED display screen with some easily readable buttons. Some models are made to be very easy to use, but you’ll have to learn how to read the graphic images once you’re all set up. 

How Does A Flasher Fish Finder Work?

Flasher fish finders are a great choice for ice fishermen or bass anglers alike. They use sonar technology to establish structures, depth, and compositions directly below the transducer. The sound wave signals are picked up by the transducer and then displayed in a flasher’s dial. This will show you where the schools of fish are hiding.

Many models will vary in features, but some of the key features would be an active display on-screen, a selection dial, target key, zoom key, and power or range dial. Flasher fish finders are also great to determine whether the bottom is hard or soft to fish more accordingly with the right lure and line.

How Does A Portable Fish Finder Work?

If your primary use is fishing from a small boat, then a portable fish finder could be the best choice. They’re small in size and weigh nearly nothing, so they're perfect for long trips or for angling travelers. These fish finders can fit perfectly into the palm of your hand and don’t need to be mounted to get good readings of fish targets.

Wireless or castable fish finders are quite new to the scene, but they work very well, especially from small boats. You can cast this device with a spinning or baitcasting rod, and you’ll receive all of the information directly to your smartphone.

How Does A Vexilar Fish Finder Work?

Vexilar is one of the most well-known and reputable brands, especially in the ice fishing community.

They excel at making high-quality fish finders that send and receive signals by a transducer suspended in the water. It displays these readings in a three-color flasher display. Green signals represent weak signals.

The color orange is for medium-strength signals, and red is reserved for only the strongest signals. The signal of the Vexilar allows you to quickly know if the bottom is rock, sand, or muck, so you don’t get into any hard to maneuver situations.

How Does A Fish Finder Work On A Boat?

If you buy a fish finder that’s suitable for a small boat, then you will have the main unit and the transducer.  That means the transducer and main unit will need to be mounted appropriately.

On most modern boats, you’ll have three choices for connecting your transducer- the shoot-through, through-hull, and transom mounts. The most popular for small boats is the transom mount, as it works well for low speeds and causes the least amount of interference.

Once you’ve installed and mounted your device, you’ll need to learn how to read the device to locate schools of fish.

People Also Ask (FAQs)

How deep do fish finders go?

Some fish finders can determine movement from 200 ft below the transducer. For maximum depth readings, use a lower frequency. 80kHz or 50kHz is a great choice for deeper waters.

Can you use two fish finders at the same time?

If you have two devices running in close proximity, then you face the risk of interference. Some modern, higher-priced models won’t face this problem and can be matched to the same frequency to another device without interference. This would be a good option for large boats.

Do fish finders work in shallow water?

Yes! There are more and more brands releasing devices that can be perfectly pitched for shallow and deep waterways. Some even have options to set the sonar frequency for ice fishing, salt, or freshwater fishing.

How do you read a fishfinder?

Understanding and learning about fish arches are important when reading a fishfinder. Larger arcs show that there’s a big fish detected. And half arches typically mean a fish has swum through a part of the sonar cone. If you see a number of these together, then you’ve found a school.

Do fish finders actually show fish?

Some brands have fish indicators on their devices, but typically the device will show signals in the form of a chart, dial, or map. Your fish finder may display baitfish in a different color to vegetation, but this depends on the model and style you choose.


With an array of choices, and models available, it's time to narrow down your search and consider which is the best fish finder for you. This guide has given you the information you needed; now it’s time to put it to use. Be sure to know your needs and pick wisely. You’ll be running into schools of fish in no time.