How Do Fish Finders Work?

Fishing Boat
Fishing Boat

FishFinders Work With Technology

The device that many fisherman rely on to find a great catch in any body of water is a FishFinder. Whether you’re fishing for leisure or sport, fishing is much more fun and productive when you actually catch fish. These sounders, as they are also called,  are small-sized computers that help you determine what is underneath and around the boat. Although fishermen have different skill levels, FishFinders make it easier to track the location of fish in the water.

Many fishermen don’t fully grasp what they’re looking at when viewing the screen of a sounder. The screen shows you a graphic visualization of the fish below, displaying the depths of nearby fish. We will discuss some of the device’s components and capabilities.

Perhaps the most important feature to consider when choosing your fish finder is the size of the screen. You want a sizeable display so that you can clearly see the information shown. As mentioned above, the device is also known as a sounder because it picks up the reflective pulses of energy in the form of sound, otherwise known as sonar.

This FishFinder technology initially emerged in the ’90s and has been continually upgraded since then. There are many different types of these tools to choose from including the standalone version, network, and combo versions. If you want a large display and the greatest performance for the price, you may want to choose a stand-alone device. This device serves only a single function.

However, you can always add on other functions by installing a GPS sensor that turns your standalone device into a chart plotter. The stand-alone option is a great choice for a smaller boat while you might want to upgrade to a FishFinder combo unit for a midsize boat.

A FishFinder combo unit is equipped with a GPS that can lead you to the fishing grounds, displaying the fish once you’ve reached the location. A networked device gives you much more intricate details and is capable of reading a larger set of data. A networked device supports GPS raster maps, vector maps, radar, SiriusXM satellite radio, and video.

Fishfinder components:

The transducer makes the magic happen and does most of the work. The transducer does the job of figuring out what lies below and around the boat, then sends the data to the head of the unit where the software interprets the data. This component does the viewing and the hearing for the device. The software of the unit takes the interpretive data and creates a graphic image to display on the screen.

The piezoelectric parts vibrate at a certain frequency sending sounds into the water. The piezoelectric parts send out a signal and then the signal is returned or echoed. The length of time it takes the signal to return and the strength it returns at converts into an electric signal which the device reads. Transducers come in different shapes and sizes; imaging sonar transducers come in a rectangular shape and 2D sonar transducers in a circular shape.

Some FishFinder transducers are equipped with CHIRP technology which modifies the frequency sent out by the transducer to include a range of frequencies instead of one defined pulse. The transducer is responsible for capturing raw data. It’s important to keep in mind that the transducer will help you find fish, but because the sonar does not discriminate you will also find random objects such as logs and rocks.

Your transducer covers more area underwater with a wider cone. Sailboats work well with hull mount transducers. Transducer cone size can range from 9 degrees to more than 60 degrees, you may find a happy medium with a 20-degree transducer cone.

GPS. When you are far away from familiar landmarks or lines of sight, you need something that you can rely on to find and return to great angling spots. The GPS completely takes the guesswork out of locating fish in open or deep water. You’ll find the GPS to be an invaluable tool when you are catching fish.

A great GPS will be able to determine the position of your boat even if you’re going at a very slow speed. The GPS makes it easy to navigate and find the best fishing areas and even return to those special fishing areas in the future. Your GPS can help map out the area underneath you if you idle over the water for a while.

As you do this, the software creates a map for you. A sounder with a GPS combo will allow you to use sonar and GPS simultaneously or you can use each component alone. The GPS makes it possible for you to create a collection of your favorite fishing spots and have the ability to navigate to them whenever you like. Kayak and boat fishermen benefit a great deal from GPS integration.

If you’re fishing on the shoreline or a pier it may be less crucial for you to have this component. Many fishermen don’t have a lot of space on their boat. Thankfully, fish finders continue to be manufactured in smaller sizes but with efficiencies and innovations.

Fishing Trophy
Fishing Trophy

FishFinder Screen Size

Display screen sizes vary from device to device. There are devices with color display screens as well as grayscale versions. With the black and white version, stronger echoes received by the transducer are darker, while weak echoes will be lighter. Resolution is provided in pixels per inch, the more pixels, the sharper the quality. With black and white screens, the resolution improves with a greater amount of pixels.

Alternatively, a color screen is going to give you far more definition and enable you to more easily tell the type of fish being displayed. The size of the display varies from 4 inches up to 10 inches; larger screens can display more information. Think about the information that is most important for you to view while fishing and how much data you would like to see at any given time. For example, if you want to see a chart plotter and your sonar side-by-side, you may want to choose a larger 9-inch screen rather than 5 inches.

Keep in mind that an increase in the size of the display decreases the crispness and sharpness of the pixel density. You may want to view a few different models side-by-side so that you can witness firsthand how pixel density decreases with the increase of the screen size. In general, a larger screen typically means more features. When making your purchase decision think about if you would most enjoy viewing data on a screen the size of a smartphone, tablet, or 10-inch laptop.

Side imaging

Typical sonar only sees what is directly underneath the boat. Side imaging sonar uses a beam that extends up to 240 feet onto both sides of the boat. This means you’re getting 480 feet of coverage on the bottom of the body of water you’re on. Sonar images don’t depend on light. Mud and darkness will not interfere with your device’s side imaging capabilities.

Your side imaging will pick up on submerged boats and cars, schools of fish, and natural structures. In side imaging mode, recent images can be viewed at the top of the screen while the image history moves down the screen. The location of your boat will be in the top center of the screen.

To understand the water column, simply fold the screen in half down the middle, in your mind. From this perspective, the dark band is the water between the surface and the bottom. Anything taking place in this water column area of the screen is occurring right underneath your boat. Side imaging is an advanced feature that provides an excellent picture of the bottom of the water. It allows you to locate far more fish than basic sonar. Side imaging goes by a different name depending on the brand.

Garmin refers to this feature as SideVu, Humminbird calls it Side Imaging, and Lowrance names it SideScan Imaging. It can be a bit daunting at first to understand what you’re looking at when viewing side imaging. If you’re not familiar with sonar graphics, simply turn the device sideways and look at the bottom half of the image.

From the top of the image to the bottom, you’re looking at the surface, water column, and finally, tree-like structures leading down to the very bottom. Simply turning your head or the device provides so much clarity regarding understanding side imaging.

Down imaging

Down imaging technology also uses side imaging to provide images of the structures below your boat. Down imaging moves from right to left with the most recent images appearing on the right-hand side. You can use down imaging in combination with side imaging and switch fire to create the ultimate fish catching tool. This display mode shows the objects and structures directly beneath the boat.

Down imaging allows you to clearly distinguish fish from other random structures in the water. It is used to provide clear graphics of exactly what is below you. It’s the best way to confirm with confidence that there are fish below you. There are many techniques to use down imaging. One technique calls for you to use side imaging to identify something of interest and then convert to down imaging for confirmation.

Down imaging also goes by many names and is referred to as DownScan, DSI, DownVu, and DownScan Imaging. This component of the device gives you a more realistic picture quality. Down imaging can give you a 180-degree view of the bottom of the body of water when combined with Side Imaging. If your finder has this feature built-in it may be labeled as DS, CV, or TI.

In short, down imaging allows you to see more fish. For example, you’ll be able to determine that there is a couple of fish swimming between the branches of a sunken tree down imaging. with traditional sonar, it’s highly likely that you will only be able to see the tree. With down imaging, your boat is on the upper right corner of the screen. If you’re fishing in waters that have a lot of structures below the surface, down imaging will help you see the fish amongst the rubble.

Fishfinder at Sea
Fishfinder at Sea

Networking Devices

Networking all of the devices on your boat is considered an advanced method. You can expect SiriusXM radio, video, GPS, and radar. Many fishers have more than one device and network them between themselves or a hub. An ethernet system is used by Humminbird, Garmin and Lowrance use NMEA 2000.

The network enables you to share GPS positions, routes, waypoints, and tracks. It’s possible to run two transducers at once as long as it’s done correctly. You no longer have to manually add waypoints on the different devices in your boat. Once you enter the waypoint into one device, it automatically transfers to the other through the network.

The ability to share sonar and GPS data across multiple devices is one of the main advantages of ethernet networking. Each unit is capable of displaying different information from GPS receivers, temperature sensors, and transducers. If you have a Humminbird device, you can enable waypoint sharing under the Network menu to begin sharing data across devices.

Reading a device. Knowing how to read a device is critically important when you are on the water. You don’t want to wait until you’re out in the boat to begin learning how to interpret the data your fishfinder is picking up. One of the features you want to learn about is the depth finder. Depending on the model you have, the depth will be displayed in the top left corner of the screen in meters.

The depth finder will tell you a lot about the type of fish in the area and what to expect underneath the boat. The depth finder shows the depth of the area directly underneath you at the current moment.

In general, you’ll find the temperature of the water just below the depth on the screen. Just with these two features alone, water temperature and depth, you can begin looking for the right environment preferred by the fish you are looking for.

Your device might even be equipped with thermocline which shows you where warm water meets cooler water. Deep pockets of water are usually colder. This is truly valuable information when you want to snag the bigger fish often swimming in deep pockets. Some fish prefer cooler waters while others are found in warm waters. The speed sensor lets you know how quickly you’re moving and functions like a speedometer.

The color displayed on the device lets you know the strength of the signal received unless you’re using a grayscale device. The stronger the echo received by the device, the stronger or darker the color will be. The seabed is usually the darkest area you will encounter. it may be a bold, thick line, meaning that the bottom is hard and not very porous. A light or thin line means that the ground is a softer material closer to clay.

To properly read your finder, you need to know what it looks like when you encounter structures, objects, fish, an object with fish around it depending on your device, you may be shown the raw data or the date of may be converted into lines, arches, and fish icons. In some cases, the fish icons will even be different sizes to convey the size of the fish detected. Once you have detected the fish icon, you’ll want to note the depth and cast to that depth.

If you don’t have fish icons on your device you may see arches. When the sonar wave from your transducer reflects off of a moving target, the symbol you see is an arch. If the object is not moving it will be represented as a line. Remember the size of the area you’re scanning for fish depends on the cone size of your transducer. Narrow cones scan between 10 degrees and 20 degrees while wide cones scan between 40 degrees and 60 degrees.

When it comes to arches, think of the length of the arch in terms of time. For example, if there is a single stationary fish underneath your boat you’ll see a single long line. The long line does not mean that you have a large fish nearby, it could be a small fish that is remaining still. There could be a big fish that swims by very quickly and this is represented as a shorter arch. A long arch does not necessarily mean a big fish.


When you’re angling with a FishFinder, fish will no longer have secret hiding places. You’ll be able to see the aquatic structures and see where fish are swimming. You can locate fish in all types of terrain, even while deep sea fishing, ice fishing, in choppy rivers, and in the rain.

Look for a unit that has the proper power voltage for the depth of water you’re in. You also may want a device with high peak wattage when in deep salty water.

You will need power to operate the device, and most operate from a 12-volt power source. Adding an in-line fuse will give you overload protection. Thanks to this technology, your fishing resultswill no longer be left to chance.

Maximize your time on the water and get the most out of every minute you spend fishing. These tools will cut down on wasted time guessing where the fish might be. There may be a bit of a learning curve the first time you take the device out. Have patience while you learn how to use this tool.

You will no longer waste precious time looking for that random spot where the fish may be hiding. You will be able to find the fish, and also save your location.

Don’t worry if you’re not technologically savvy, you just need to spend some time familiarizing yourelf with this great tool. The contribution this fishfinder will make to your boat is unmatched. We wish you much success in your future fishing adventures with whatever brand you choose.

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