How Fish Finders Work?

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It’s 2023, and having a fish finder is more than a luxury, it is a necessity. If you have ever wondered how fish finders work? You are at the right place!  This blog takes you beyond those  LCD screens and crisp bright images to provide clear insights on how fish finders work? 

For freshers – Fish Finders are electronic devices used by anglers to locate fish underwater.  They  provide real-time data on water depth, fish presence, and underwater terrain, improving fishing efficiency and increasing the chances of a successful catch. Now let’s dive into the topic and understand the basics.

How Do Finders Work: The Basics

Modern day Fish finders work through  SONAR Technology. Also called as SOund NAvigation Ranging , it is a method where a pulse of sound waves is passed down the water. These waves hit the bottom or any objects in their pathway and reflect back. The Sonar device measures the time required for the sound waves to travel down,  hit an object and then bounce back up. Based on this information the fish finders judge the depth and the objects below the water. It can also measure the strength of the returning pulse helping you catch a big fish. 

But, how is it made possible in real time in new fish finders?  

Now let’s get behind the technology that works on the principle of sonar waves and echo detection. It all starts with a transducer.



The core component of a fish finder is the transducer. This device converts electrical energy into sound waves and vice versa. 

It is typically mounted inside the boat, mostly at the bottom and is submerged in the water. 

The transducer emits a cone-shaped beam of high-frequency sound waves into the water.

Sound Waves

The fish finder transducer sends out a continuous stream of high-frequency sound waves, usually in the range of 50 kHz to 200 kHz, depending on the model and the desired depth of scanning. 

These sound waves travel through the water in a cone-shaped pattern, with the width of the cone determined by the transducer’s design and settings. This might change when you use a fish finder.


When the narrow beam of sound waves encounter objects or changes in the underwater terrain, such as fish, rocks, or vegetation, they bounce back towards the transducer as echoes. 

The time it takes for the sound waves to hit the object and vibrate back to the transducer is used to calculate the depth and location of the object.


The fish finder’s display unit, often a screen, receives the echoes returned by the transducer. It processes the Sonar data and creates a visual representation of the underwater environment. This display can show various details, including the depth of the water, the composition of the bottom (mud, sand, rocks), and the presence and location of fish and other objects.


Fishermen can interpret the information displayed on the screen to identify fish schools, individual fish, and their depth. Different fish species and sizes can be distinguished based on the strength and size of the echo returns. The display may also include features like fish icons and depth readings to make it easier for users to understand the information and step up their fishing game.


The symbols represent the objects and the numbers represent the depth from the surface of the water. For better understanding let’s have a look at a case study.

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How Fish Finders Work: A Case Study With Garmin ECHOMAP UHD 94sv

Stage 1: Sonar Transducer

 Garmin ECHOMAP UHD 94sv fishfinder consists of a transducer. This transducer is usually mounted on the bottom of your boat’s hull, and it is responsible for emitting and receiving sound waves. The Garmin ECHOMAP UHD 94sv uses CHIRP (Compressed High-Intensity Radiated Pulse) sonar, which is an advanced form of sonar technology.

Stage 2: Emission of Sound Waves

The sonar transducer emits a continuous range of sound waves into the water. These sound waves are sent at different frequencies, creating a broader spectrum of coverage compared to traditional sonar that covers a smaller area.

Stage 3: Sound Wave Propagation

As the Sonar works it emits  sound waves traveling downward through the water in a cone-shaped beam. This cone widens as it descends, allowing the device to cover a larger area beneath your boat.

Stage 4: Reflection of Sound Waves

When the sound waves encounter objects in the water, such as fish, submerged structures, or the sea floor, they get reflected back toward the transducer. The time it takes for these reflected sound waves, or echoes, to return to the transducer is recorded.

Stage 5: Signal Processing

The Garmin ECHOMAP UHD 94sv’s onboard computer processes the returning echoes. By analyzing the time it took for each echo to return and the strength of the echoes, the device can determine various characteristics of the underwater objects.

Stage 6: Display

The processed data is then displayed on the high-resolution touchscreen of the Garmin ECHOMAP UHD 94sv. The screen shows a visual representation of the underwater environment, with fish, structures, and the sea floor displayed in different colors and symbols for easy interpretation.

How Fish Finders Works

Types of Sonar Technology Used in Fish Finders

As previously covered, SONAR technology in Garmin fish finders uses sound waves to locate objects underwater. It emits a signal, listens for echoes from fish or structures, and calculates their positions based on the time it takes for the sound to bounce back. This enables users to locate and track fish in the water.

  • Description: 2D sonar, also known as traditional sonar, employs a single frequency and emits a circular beam into the water. It’s the most basic type of sonar and provides a straightforward representation of the underwater environment.
  • Application: 2D sonar is effective for showing the overall depth and contour of the water, as well as locating fish and structures in a broad area. It’s a versatile choice for general fish finding and depth measurement.

Description: CHIRP sonar is an advancement over 2D sonar. It utilizes both high and low frequencies to transmit a range of frequencies in a continuous pulse. This results in a more comprehensive view of the underwater world with a circular beam.
Application: CHIRP sonar provides improved target separation, enhanced clarity, and a better understanding of the underwater environment. It’s effective for detecting fish and structures with greater detail and accuracy.

  • Description: Down imaging sonar features a rectangular-shaped beam that provides finer, narrower detail compared to circular beams. It’s well-suited for showcasing underwater structures and objects.
  • Application: Down imaging sonar is ideal for anglers who want a more detailed view of what’s beneath their boat. It excels at revealing submerged vegetation, rock formations, and individual fish with precision.
  • Description: Side imaging sonar scans sideways with a fan-like angle, offering a wider view to the sides of the boat. It requires boat motion to create a comprehensive image.
  • Application: Side imaging sonar is excellent for detecting structures like weed beds, rocks, and submerged objects. Anglers can use it to identify fish-holding spots along the sides of their boat’s path.
  • Description: 360° imaging sonar is a powerful tool that rotates 360 degrees to scan all directions around the boat. It’s particularly useful in shallow waters where structures and fish may be scattered.
  • Application: This technology helps anglers spot structures and fish in all directions, providing a complete view of the underwater terrain. It’s valuable for identifying potential hotspots.
  • Description: Live sonar provides real-time sonar returns, offering a dynamic view of underwater activity. It shows fish reactions to bait and lure movements.
  • Application: Live sonar, often referred to as ‘video game fishing’, is ideal for anglers looking to closely observe fish behavior and reactions. It’s particularly useful in vertical fishing scenarios, such as ice fishing or drop-shotting.
  • Description: Forward-facing sonar displays a live view of what’s ahead of the boat. It’s typically mounted on a trolling motor for a forward perspective.
  • Application: This technology helps anglers navigate and identify underwater structures and fish in front of the boat. It’s useful for precise casting and avoiding obstacles in shallow waters.

Water Depth Limitations

Fish finders have depth limitations that can affect their accuracy and the ability to detect fish and structures. For the Garmin ECHOMAP UHD 94sv, it’s essential to consider that while it excels in a wide range of depths, deeper waters may require different frequency settings to maximize performance.

Garmin ECHOMAP UHD 93sv  offers high-quality transducer and advanced sonar technology, but it may be a more cost-effective option if you primarily fish in shallower waters.

Transducer Quality

 The quality of the transducer is crucial in determining the clarity and accuracy of fish and structure detection. The Garmin ECHOMAP Ultra 126sv is an exceptional choice if you’re looking for top-tier transducer quality. It features a high-performance transducer that provides incredibly clear and detailed sonar readings, ensuring accurate fish and structure detection.

Frequency Selection

 Different frequencies are suited to different water depths. Higher frequencies are ideal for shallower waters, while lower frequencies are better suited for deep-sea fishing. For anglers who frequently switch between shallow and deep waters, the Garmin ECHOMAP UHD 73sv offers versatility. Users must adjust the frequency settings to match their fishing environment.

Water Clarity

Water clarity plays a significant role in the performance of fish finders. Clear water allows for better sonar signal penetration and accuracy. In contrast, murky or turbid water conditions can scatter sonar signals, reducing the effectiveness of the device. The Garmin ECHOMAP UHD 94sv’s advanced sonar technology is designed to work optimally in various water conditions.


Electronic interference, whether from other onboard devices or nearby boats, can disrupt sonar signals and lead to inaccuracies in readings. To minimize electronic interference, consider the Garmin ECHOMAP UHD 75sv. This model includes features and shielding that help reduce interference, ensuring that sonar signals remain clear and accurate, even in busy marine environments.

Cable Length

The quality and length of the cable connecting the transducer to the fish finder can affect the strength and clarity of the sonar signal. Longer cables risk signal loss, which can impact the device’s performance. Users should ensure that the cable is of high quality and an appropriate length for their setup. For installations requiring longer cable lengths while maintaining signal integrity, the Garmin ECHOMAP UHD 73sv offers flexible cable options.

Temperature Variations (Thermoclines)

Sudden temperature changes in the water, known as thermoclines, can alter sound wave propagation and affect the accuracy of fish finder readings. The Garmin ECHOMAP UHD 63cv is a reliable choice for anglers who frequently encounter thermoclines. It’s equipped with features that assist in interpreting temperature variations and adjusting fishing strategies accordingly.

Fish Behavior

Fish finders detect fish concentration and location, but the behavior of the fish can impact the readings. Tightly schooled fish can create dense sonar signals, while more dispersed fish may appear as individual targets.  The Garmin ECHOMAP UHD 75sv offers detailed sonar capabilities that help distinguish between tightly schooled fish and dispersed fish, providing valuable insights for successful fishing.

User Knowledge

Operator understanding of fish finder settings, such as sensitivity, frequency, and cone angle, tailored to the specific fishing environment, is crucial. To enhance user knowledge and fine-tuning capabilities, the Garmin ECHOMAP UHD 73cv is a versatile choice. It allows operators to adjust sensitivity, frequency, and cone angle settings to match their specific fishing environment.

Sonar Cone Angle

Fish finders offer different sonar cone angles, and users can select from wider or narrower cones. Wider cones cover more area but provide less detail, while narrower cones offer finer detail in a smaller area.   For users who require different sonar cone angles, the Garmin ECHOMAP UHD 95sv offers versatility. It allows you to choose between various cone angles, optimizing coverage area or detail based on your fishing preferences.

Practical Tips for Using Garmin Fish Finders

  • Familiarize yourself with the fish finder’s functions and settings by reading the user manual.
  • Ensure the transducer is correctly mounted, parallel to the water’s surface, and free from obstructions.
  • Match the depth range setting to your fishing area for precise readings.
  • Adjust sensitivity to balance clutter reduction and fish detection effectively.
  • Select between fish symbols and arches based on your preference and experience.
  • Use GPS features for marking productive spots and navigation assistance.
  • Learn how to use the zoom feature to focus on specific depth ranges or targets.
  • Regularly clean the transducer and inspect cables for damage to maintain optimal performance.
  • Try different settings in various fishing conditions to enhance your interpretation of readings.
  • While using the fish finder, remain attentive to water and surroundings for a safe and successful fishing experience.


Garmin fish finders have revolutionized underwater exploration for anglers. Leveraging advanced sonar technology, these devices provide essential data on water depth, fish locations, and bottom structures.

Ongoing advancements have introduced high-definition imaging, seamless GPS integration, wireless connectivity, and more, enhancing their versatility. Whether you’re a novice or an experienced angler, a fish finder significantly boosts fishing efficiency, enabling precise fish tracking and ensuring more successful outings.

As innovation continues, fish finders remain indispensable tools for modern fishing and boating adventures. Explore the depths of this technology to elevate your fishing experience.  Take a stroll on our website and reach out to us for more information. 

Gary Burrell

Chief Content Writer and Reviewer at Garmin Fish

Born in 1989, Gary Burrell is an Electrical Engineering graduate from the University of Tennessee. With 20+ years of experience, he has transitioned from engineering roles to becoming the Chief Content Editor. Gary’s unique blend of technical knowledge and editorial expertise has made him an essential figure in content creation, ensuring clarity and accuracy. His journey from an engineer to an editor showcases his adaptability and commitment to continuous learning.