What Are Fish Finders and How Do They Work

What Are Fish Finders and How Do They Work

Fishing has been around since humans first stepped foot on earth, as a means of securing survival through food. As we evolved, our inventions and technology evolved with us and translated into creating intuitive, more effective tools to carry-out our different activities.

It’s no surprise that modern technology found its way to modernize fishing equipment that gives us more information to use at our disposal and helps us achieve better results. 

As their name suggests, fish finders are devices that help anglers locate fish and give them a tactical advantage to plan ahead and tackle different fishing environments.

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What are Fish Finders

Fishfinders, at their core, are an application of sonar (Sound Navigation and Ranging.) Sonar uses sound waves to paint a picture of your surroundings. Moreover, most of the fish finders on the market have a built-in GPS. With data from both systems, you can identify the perfect spot to place your baits.

For a fish finder to operate properly, there should be a synergy between its two primary components: the head unit and the transducer. 

As we discuss the different components of the fish finders in more detail, you will have a better idea about each part’s role and how they all add up to the fundamental principle upon which fish finders operate.

Components of a Fish Finder

1. Transducer & Head Unit

Transducers send acoustic signals down into the water. When the sound waves hit any object or surface, they are reflected and picked up by the transducer. So, you can think of the transducers as eyes or ears that pick up sensory information and connect the angler to the surrounding environment.

The head unit of the fish finder then comes into play. It functions as the brain whose job is to make sense of the returned signals and translate such waves into information anglers can use.

2. GPS

Fishfinders integrate navigation systems to give you an extra layer of spatial awareness. The GPS, in most cases, is accurate enough to detect your boat’s location even if you’re moving at slow speeds.

Being able to pinpoint your location opens up a lot of possibilities, like the ability to add custom waypoints. With the GPS in place, you can return to your favorite spots in future fishing trips.

3. Screen

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The fish finder’s screen is your means of interaction with the sonar system. You will be presented with the information that has been collected in the background by the transducer and interpreted by the head unit.

When choosing a fish finder, you should consider the screen’s size and pixel density. Bigger screens allow you to review more real-time information at a glance without having to scroll through menus. 

The next aspect to consider is the pixel density. Screens with a higher pixel density give you crisp images and allow you to spot even the finest details. 

We recommend that you see the screen for yourself before finalizing your purchase decision and decide which size and resolution work best for you.

4. Local Networking Systems

Professional anglers can simultaneously use multiple fish finders that are placed at different spots on the boat. One is usually placed near the steering wheel, and the other is close to where the angler will be casting.

In this setup, you want information from the different fish finders to be superadded and to give you a panoramic view of your surroundings. Fish finders of the same brand are more likely to connect to one another seamlessly. If this is not the case, you can use a hub to set up a local network for all of your fish finders to relay information to.

If you have a large boat and you’re planning to use multiple fish finders, you need to check the networking features before committing to your purchase.

Fish Finder Power

The fish finder’s power is measured in terms of watts RMS (Root Mean Squared.) The power is directly proportional to the maximum depth that the sound waves can travel to. Also, it influences how well the fish finder can distinguish individual objects like rocks and plants, and tell them apart from nearby fish.

A 200-watt RMS fish finder will be more than enough if you are targeting lakes and inland water bodies. For coastal waters, we recommend you pump the power to 500 watts. Finally, for blue waters, you will need a robust fishfinder with 1000 watts to transmit powerful waves that can travel all the way to the very deep water beds.

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Types of Fish Finders

Fishfinders can be classified according to how many wave frequencies their transducers are able to produce. Some transducers only emit waves with a single specific frequency, while others can alternate between a range of frequencies at the same time.

1. Side-Imaging Transducers

Those transducers send ultra-thin beams of acoustic waves at 180 degrees to cover large areas around your boat. The side-imaging transducers can send waves up to a distance of 240 feet in a given direction.

As the boat moves, the returning waves are added on top of one another to map the lake’s bottom. If your fish finder has an integrated GPS as well, you can mark locations on the map that have been put together by the side transducers.

Side-imaging fish finders are an example of transducers that emit one frequency of waves, whether high or low. We recommend you pick a model that uses high-frequency waves for side-imaging. It will give you a crisp, detailed look at the water bed’s topography, in addition to any changes in depth or the bottom’s rocks and plants.

It’s difficult to identify fish on side-imaging graphs. After the sound waves hit a fish and reflect, they will show up as bright spots on the side-imaging photos. Those spots can be easily missed if the fish is close to the bottom, as waves from the bottom will blend with the reflected waves from the fish, and your potential catch can be concealed in plain sight.

2. Down-Imaging Transducers

The transducer emits narrow beams of high-frequency waves at 90 degrees to face directly downwards and show you what’s going on under your boat.

The reflected waves will then be used to put together a 2D sonar image of what’s exactly below your boat. It’s easier to spot fish using those 2D images compared to their counterparts from the side-imaging fish finders. 

Tip: Put in mind that the fish will appear smaller than they actually are since down-imaging transducers use narrow beams.

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3. Dual-Beam Transducer

The transducer emits waves at two different frequencies. Waves with lower frequencies can cover larger areas and allow deeper sonar penetration, while those with higher frequencies are only capable of concentrating over narrow surface areas. However, they tend to create more detailed, higher-resolution images.

Since dual-beam transducers use waves with frequencies on both ends of the spectrum, the end results are more detailed images covering a wider surface area.


Broadband fish finders have the acronym CHIRP for Compressed High-Intensity Radar Pulse. Instead of transmitting waves with one or two frequencies like the systems we discussed above, CHIRP are unique in that they can send signals covering a range of frequencies.

With their broadband waves, CHIRP can put more energy into the water, 10 to 50 times more than the conventional fish finders. Also, they can send waves for a longer duration. 

The collected information is then processed into images with unprecedented details. CHIRP have the upper hand over conventional ones, as they can pick fish inches away from the bottom. Traditional fish finders will miss on those and consider them as part of the bottom’s topography.

Moreover, when CHIRP fish finders pick on a group of fish, they can identify each one of them separately. In contrast, traditional fish finders identify the whole group as a single mass.  

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Final Thoughts

Remember that fish finders like fish finder for ice fishing and the outher types are not meant to catch fish for you; they are just tools that provide you with data. Learn how to use that spatial awareness to your advantage, and be flexible with your fishing technique according to the situation.

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