How Does a Fish Finder Work: Fish Finder 101

New to fishing and fish finders? If so, you’ve come to the right place. In this Fish Finder Buyer’s Guide, I’ll help you understand how fish finders work and how to read them.

What is a Fish Finder?

Lowrance HOOK Reveal 7x SplitShot - 7-inch Fish Finder with SplitShot Transducer, GPS Plotter

Fish finders are devices that emit sound waves into the water in order to determine the location of fish. The device then uses this information to generate a display, which helps anglers locate and catch fish.

Kiyaotaka and Kiyokata Furuno invented the technology of detecting fish underwater in 1948. And after years of innovation, fish finders today can be used in both fresh and salt water, and come in a variety of shapes and sizes. Some fish finders are portable and can be handheld, while others can be permanently mounted on a boat.

In addition to that, fish finders use different types of technology to create their displays. Some use sonar, while others use GPS or other satellite-based systems.

Best-Selling Fish Finders on Amazon

How does a Fish Finder Work?

Basically, fish finders work by sending out a sound wave that bounces back when it hits something solid, like a fish. The device then uses this information to create a picture or a sonar image of what is beneath the surface. This can help fishermen to identify where fish are swimming and what type of bottom they are swimming over.

Parts of a Fish Finder

To be able to fully understand how fish finders work, let’s discuss first the different parts of a fish finder.

Parts of a Fish Finder #1: The Transducer

LOWRANCE HDI/CHIRP SKIMMER Wide Beam Coverage 83/200 khz and Down Imaging 455/800 khz Fishfinder Transom Mount Transducer

A transducer is the main component of the fish finder. It is usually used in automation, control systems as it works by converting energy from one form to another.

Transducers uses SONAR (Sound Navigation and Ranging) technology to convert electrical signals into light, motion, sound, and other forms of energy, making it an integral component of any fish finder.

How does a Transducer detect fish?

The transducer is the component of the fish finder that emits and receives the sound waves used to detect fish. The transducer converts electrical energy into sound waves, which are then sent into the water.

When the sound waves bounce off of a fish, they are reflected back to the transducer. The transducer then converts the sound waves back into electrical energy, which is used to create an image of the fish on the screen of the fish finder.

How do Transducers differentiate fish from other structures underwater?

Transducers are able to distinguish between fish and other debris underwater because they can sense the air bladder of the fish. The air bladder organ of the fish has gas fillings and enables the fish to adjust to the water pressure at different levels of depth. This process regulates the buoyancy level of the fish.

Because of this, the density level of the air bladder is different as it contains gas. The density will be different than the other parts of the fish as well as other objects in the water. This unique aspect of the fish makes the sound echos bounce off differently than the other objects.

What is a Transducer made up of?

Fish finder transducers are usually made up of tiny piezoelectric crystals that are mass-produced in large labs. And Barium Titanate or Lead Zirconate Titanate are the primary materials used in making these crystals.

The crystals work by growing or contracting when exposed to electric currents. These crystals vibrate when it hits an object creating sound waves in return. When crystals vibrate, expand, and contract, it produces sound or echo.

The Piezoelectric crystals or elements come in the form of a disk, bar, or ring. These crystals are linked together to form an array and the more extensive the crystals are, the more noise it produces. This loud noise helps gather definite information.

Parts of a Fish Finder #2: The Display

Garmin 010-01550-00 Striker 4 with Transducer, 3.5' GPS Fishfinder with Chirp

The display is another integral part of a fish finder. The display screen provides all the information gathered by the transducer, including water depth, speed over water, temperature, and fish location and types, etc.

the fish finder come in different shapes and sizes. The bigger the screen, the more information is on display. However, smaller screen fish finders are more portable. Higher pixels and HD screen mean crystal clear display.

Parts of a Fish Finder #3: GPS and Chartplotters

Simrad NSS12 Evo3S - 12-inch Multifunction Fish Finder Chartplotter with Preloaded C-MAP US Enhanced Charts

The modern fish finders have an inbuilt GPS. The GPS enables you to track your location on waypoint maps and navigate around. Other features like the temperature, speed, and depth of the water are also available. This feature makes fishing a pleasant and exciting experience.

The GPS on your fish finder can chart your position and point it out on a map. An internal GPS receiver is common in use. But an external receiver can show boat’s position and their direction even at slow speeds. A good the fish finder gets used for scouting, navigating, and making waypoints for future.

Parts of a Fish Finder #4: Connectivity

Venterior Portable Rechargeable Fish Finder Wireless Sonar Sensor Fishfinder Depth Locator with Fish Size, Water Temperature, Bottom Contour, Color Display

The modern-day fish finders come with connectivity options such as Wi-fi, Bluetooth, and others. These options enable you to connect the device with smartphones, tablets, and other fish finders without the use of a cable.

Types of Fish Finders

Whether you are a beginner or an expert in fishing, you will always want this piece of supreme technology to help you. Fishing is not just lazing around with a stick. It is a sport that shows perseverance and patience. So why not use the best technology for the best experience of this beautiful sport?

There are basically two types of fish finders according to the types of SONAR technology:

Basic Sonar

SONAR Technology Fish Finder

Traditional SONAR technology works by producing a sound wave or pulse energy and sending them to the water. Sound waves that are usually high in power or high frequency will have a short duration or can’t penetrate deeply into the water. But, higher frequencies give you a narrower cone angle that provides you with the image in great detail.

On the other hand, lower frequencies provide greater depth penetration but fewer details. The only downside is that the lower range has limited sensitivity or will produce fewer details.

That’s why most conventional SONARs use dual or triple frequencies around 50khz and 200khz to get the most accurate details.

CHIRP Sonars

The CHIRP sonars or the broadband sonar operate in a broader range of frequencies.

The CHIRP (Compressed High-Intensity Radiated Pulse)technology-induced sonars on a fish finder is a relatively new development. In fact, CHIRP sonar technology was initially developed for military purposes.

These sonars provide increased functionality and accuracy. The traditional sonar uses a single frequency for a short period, whereas the CHIRP sonar uses varying frequencies for a longer time. In fact, the CHIRP sonar puts more energy into the water to produce broadband frequency up to 117 kHz.

How does a CHIRP fishfinder work?

Traditional 2D sonars use a single select frequency. The CHIRP sonar uses an extensive range of varying frequencies.

In CHIRP fish finders, the transducer vibrates at a low frequency. The lower frequency makes the transducer modulate in higher pulses.

Generally, the higher pulses are ten times the duration of the pulse. The energy transmitted in the water is 10 to 60 times the traditional sonar. This unique pulse compression and pattern correlation feature makes it shine brightly and computes the raw data into definitive information.

In addition, the CHIRP sonar can also compress and transform a high-frequency pulse into low-frequency pulses of multiple ranges. This feature of a CHIRP sonar increase resolution and improves the signal-to-noise ratio.

That’s why CHIRP sonar delivers almost photographic images. Likewise, they also provide exceptional target separation and decrease water column clutter.

High CHIRP vs. Medium CHIRP


High CHIRP frequencies (150-240khz) help to lure, identify, and track down baitfish and gamefish. They are best suited for freshwater and inland depths less than 600 feet.

Medium CHIRP

The medium CHIRP has a range of 80-160khz. They are excellent at scanning extensive areas and showing massive fish arches. However, the detailed information provided is less compared to high CHIRP.

Best-Selling Fish Finders with CHIRP on Amazon

The next types of fish finders use a higher quality SONAR technology like CHIRP to produce the best details. The only difference is the way they scan and their purposes.

Down Imaging Fish Finder

Down Imaging Fish Finder

Down Imaging or Down Scan Fish Finders are primarily used if you want to get a good picture of what lies beneath your fishing vessel. This type of fish finder is best for bait or stationary fishing or if you’re fishing in deep waters.

Down imaging provides you with a very detailed display. It allows you to see sharper and clearer images allowing you to distinguish fish from other objects or structures underneath.

Most down imaging fish finders have a maximum depth of 300 ft. and operate at 455 kHz frequency.

Side Imaging Fish Finder

Basically, the Side Imaging or Side Scan Fish Finders are attached to both sides of the boat at the right angle direction. Side Imaging Fish Finder has 2 sonar beams and picks up any activity on each side of your boat including the fish movements or any other objects like the bait or other natural structures, wreckage parts, etc.

Side Imaging fish finders usually use 100 to 500 kHz frequencies and are best for fishing in shallow waters. And because of their shaper display, they work on both clear water, saltwater and muddy water.

With a total coverage area of 300 feet, you can scan out what parts of the water have great fish density and enjoy your best fishing experience with the best side imaging fish finder.

Now that you know, the parts and types of fish finders, let’s proceed to the next thing you should know about fish finders.

How to Read a Fish Finder

Reading a fish finder is not as hard as it sounds. The fish finder provides us with an approximate estimate of the depth of water and the shape of the bottom. Fishfinder helps us in choosing the best lure, weight, rods, and fishing equipment. You can also avoid snags.

While the average fish finders work entirely giving you proper information about the fish and water depths. Also, the advanced models are incredibly accurate and regularly updated. These devices can differentiate between the type of fish, along with providing precise fishing information.

How to Read Fish Finder

The fish symbol feature of a fish finder helps to distinguish between fish, rocks, vegetation and other debris.

Moreover, the distance between the boat and the fish are continuously changing as the fish swims around. In such cases, a fish id symbol on the fish finder lightens up. The fish id symbol is that of an arch. Hence, you can easily distinguish between fish and other objects through the help of a fish finder.

Fish Finder Buyer’s Guide

So, what type of fish finder should you buy?

First, consider the type of fishing you’ll be doing. If you’re mostly going to be fishing in shallow water, you won’t need as sophisticated of a fish finder as someone who plans to fish in deep water.

Second, think about the features that are important to you. Do you want a fish finder with GPS? Do you need one that can track multiple fish at once?

Third, take into account your budget. Fishfinders can range in price from around $100 to $1000 or more.

There are a lot of affordable fish finders available today for beginners but they will have fewer features compared to premium fish finders.

If you have the budget, I’d recommend that you buy the best fish finders equipped with the latest technology to make your fishing more enjoyable.

So, what are the things you should consider when buying one? In this section, let’s discuss the best features to look for when buying a fish finder.

Best-Selling Fish Finders on Amazon

SONAR Technology

If you’re new to fishing, you’d naturally go for something more affordable. Luckily, there are CHIRP fish finders today available for less than $500 today. Here are several reasons why you should consider CHIRP sonar.

Advantages of a CHIRP sonar

Humminbird 410220-1NAV HELIX 5 CHIRP DI (Down Imaging) GPS G2 NAV Fish Finder
1. Provides a clear representation of water bodies

The display of the bait in the water is exceptional compared to that of a traditional sonar. CHIRP sonar provides distinct target separation. This trait also enables you to differentiate well between the bait and the weight while drop shooting.

2. Facility to categorize fish

CHIRP sonar on a fish finder provides you with a better image clarity that allows anglers to classify and categorize fish. Also, this feature helps a lot to commercial fishers who like to separate and organize terror fish for selling purposes.

3. Extensive view

The CHIRP sonar uses multiple frequencies for a long duration of time. Likewise, this characteristic helps an angler to have a clear picture of the underwater environment. Moreover, anglers can also learn how gamefish relate to baitfish. It gets pretty difficult to separate the bass and stripers with the baitfish underwater.

4. Reduces noise in the final image

Another essential feature of CHIRP is that it reduces noise to a greater extent. Also, traditional fish finders use high single-frequency sonar. The display features a lot of noise on the screen.

The noise comes along with the images, and any attempt to reduce noise also reduces essential targets. The CHIRP sonar address this problem by showing filtered target images through crisp and noise reduced display.

5. Depth capability

The CHIRP sonar is better than the traditional sonar at any given standard depths. At higher depths, the CHIRP sonar performs way better. CHIRP sonar uses a long pulse duration. They also modulate and use multiple frequencies. This feature provides higher resolution and noise-free images at great depths.

CHIRP fishfinders provide almost photographic sonar images of the environment underneath your boat. The bright display of the fish and other objects is miles ahead of the traditional and down scan sonar.

Both traditional sonar and down scan sonar provide exceptional services to anglers. However, the CHIRP sonar is a significant upgrade from traditional sonars. They come packed with features like superb target separation, noise reduction, high-resolution display. Also, the CHIRP sonar is worth all the hype.

Transducer Mounting

The other factor that needs consideration when buying a fish finder is the mounting choice of the transducer. The mounting decisions can affect the working condition of the fishfinder. The in-hull, through-hull, and transom mounts are the three popular mounting choices.

How to install and mount a Transducer? | how does a transducer work for a fish finder

In-hull mount

The in-hull transducers work with any engine. The in-hull mounts perform well on both power and sailboats. The only downside is that thick aluminum hulls are not suitable for in-hull installations. This drawback is because the signals can get lost in transmission through the metal. The mount is not suitable for wooden or cored fiberglass hulls.


Thru hulls provide the best signal quality and offer the very best performance at all speeds. The shaft passes through a hole in the bottom of the hull. Also, they are quite challenging to install. They also have the least amount of turbulence. Lastly, the only downside is that you will need to cut a hole to fit.

Transom mounts

Transom mounts are best for slow speeds. The only drawback is that they often lose important details in the process. Some users have found them to not work once the boat is on a plane surface. It is because of the turbulence created by the hull, transom, and strakes. If the transom mounts have appropriate mounting, they should work fine at slow speeds. And it could give 80-90 percent performance at high speeds.

Transducer Materials

Different mounting systems will require different types of transducer materials. For casual fishing, a plastic mount will suffice. But if you’re using an in-hull or thru-hull transducer you will require different types of mounts and casings:

  • Fiberglass/Metal hulls: Use Plastic housing
  • Fiberglass/Wood hulls: Use Bronze Housings
  • Aluminum/Steel hulls: Use Stainless steel housing


Another main feature you should be looking for in a side imaging fish finder is the screen display. We are using the fish finder in order to have a clear view of the underwater movement. So it would be a waste if the product couldn’t provide us with a clear display.

The display also means color or monochrome. The colored display is much more contrasty and better than monochrome but expensive.

Display Size

Additionally, fish finders come in a variety of sizes ranging from 4 to 12 inches. The screen display is usually measured diagonally from the left bottom corner to the right top corner.

There is no definitive answer when it comes to the best display size for a fish finder. It ultimately comes down to personal preference and what you feel most comfortable using.

Smaller display sizes may be easier to use in smaller boats but reading small text and data will be very difficult because of the small screen.

Larger displays, on the other hand, may provide more detailed information but they usually are more expensive and will require more battery.

Ultimately, it is up to the individual fisherman to decide what size display works best for them.

Water Resistance

Most fish finders are already IPX7 waterproof. This means that they can survive splashes or can be submerged for up to 1 meter for 30 minutes. Some more affordable fish finders come in IPX6, which can also resist high-pressure, heavy sprays of water but investing in an IPX7 fish finder is the wiser choice.


If you’re serious about fishing, then you need a fish finder. A fish finder will help you locate fish in the water so you can catch them. The best fish finders on the market should be packed with the best features tackled in this article.

So, what are you waiting for? Get out there and buy the best fish finder for your needs!