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Deep Dive: How Does a Fish Finder Work?

Fish finders have revolutionized the world of fishing, making it easier for anglers to locate and catch fish more efficiently.

These innovative devices use cutting-edge technology to detect underwater structures, schools of fish, and other hidden features beneath the water’s surface. By understanding how fish finders work, individuals can improve their fishing experience and increase their chances of a successful catch.

In this guide, we’ll walk you through the process of how fish finders work, so you can make more informed decisions about where to cast your lines and increase the likelihood of a successful catch!

how does a fish finder work

Understanding Fish Finders

Fish finders are electronic devices used by anglers to locate and identify fish beneath the water’s surface. They operate by sending out sound waves, which bounce back when they encounter objects like fish or underwater structures.

Types of Fish Finders

There are several types of fish finders on the market, each with different features to meet the specific needs of an angler. Here are the most common types:

  • Stand-alone fish finders: These are basic units that can be mounted on a fishing boat and provide essential depth and fish-finding information. They are an excellent option for small boats and budget-conscious anglers.
  • Combination fish finders: Also known as multi-function displays (MFDs), these units combine multiple features into one device, such as GPS navigation, depth sounders, radar, and more. They can be useful for anglers who want a single, integrated solution for their boat.
  • Networked fish finders: These advanced systems allow for data sharing among various devices on the boat, including fish finders, radar, chart plotters, and more. They tend to be more expensive and are typically found on larger boats and vessels with professional anglers.

2D Sonar Versus Down Imaging and Side Imaging

Fish finders use different types of sonar technology to provide underwater imagery. Understanding the differences between these sonar types can help anglers choose the best fish finder for their needs:

  • 2D Sonar: This is the traditional sonar technology that has been used in fish finders for years. It provides a two-dimensional representation of the water underneath the boat, showing fish as simple arches or lines. While it provides valuable information about the depth and location of fish, it can be limited in showing the structure or details of the underwater environment.
  • Down Imaging: This type of sonar technology uses high-frequency sound waves to create a detailed, picture-like image of the water column and structures beneath the boat. It allows anglers to see fish within a structure and helps to identify specific types of cover or underwater habitat. However, its range is more limited compared to 2D sonar.
  • Side Imaging: As the name suggests, this technology scans the area to the sides of the boat, providing a wide, horizontal view of the underwater environment. It can be particularly useful for locating large schools of fish or identifying the composition of the lake or river bottom. On the downside, it may not provide as much detail about individual fish compared to 2D sonar or down imaging.

Detailed Components of a Fish Finder

A fish finder consists of several components that work together to provide an accurate depiction of the underwater environment.


The mount is an essential part of a fish finder, as it secures the device to the boat and ensures that readings are taken from a stable position.

There are different types of mounts available, such as transom mounts, trolling motor mounts, and through-hull mounts, each offering unique benefits depending on the user’s needs.


The display is the visual interface of the fish finder, presenting the data gathered by the device in an easy-to-understand format. High-quality displays are crucial for clear and accurate readings, especially in bright sunlight or low-light conditions.

Displays can be monochrome or color, with the latter offering better visibility and contrast. The size of the display is also a factor to consider, as larger screens allow for better readability and more detailed images.


GPS functionality is an advantageous feature found in many modern fish finders. It enables users to mark fishing hotspots, create routes, and track their location accurately.

GPS integration also allows for detailed mapping capabilities and the overlay of fish-finding data onto maps, providing a comprehensive view of the underwater terrain and fish activity.

Temperature Sensor

A temperature sensor in a fish finder is beneficial for locating fish, as they often prefer specific temperature ranges for feeding and breeding. This sensor measures the water temperature at various depths and displays the data on the screen. Understanding the temperature patterns can help anglers target fish more effectively.


The resolution of a fish finder refers to the number of pixels on the display, which determines the clarity and detail of the images shown.

Higher-resolution displays offer a more detailed and precise representation of the underwater environment, making it easier for users to identify fish, structures, and bottom contours. A higher resolution is especially important when using advanced features like side-imaging and down-imaging technology.

How Sonar Technology Works

Sonar technology, also known as SOund NAvigation and Ranging, utilizes sound waves to explore underwater environments and measure depth.

These sound waves are emitted by the fish finder’s transducer and travel through the water until they encounter an object or the bottom. Once the sound wave hits an object, it bounces back to the transducer and the time delay is recorded. This information is then used to determine the water depth and the location of underwater objects.

The depth finder in a fish finder emits a series of sonar signals into the water. These signals are comprised of different frequencies that allow for accurate depth measurements and better identification of objects. CHIRP sonar (Compressed High Intensity Radar Pulse) is a technology that sends multiple frequencies in a single sonar wave, resulting in increased clarity and detail on the fish finder’s LCD screen.

Different fish finders utilize a variety of sonar technologies to achieve specific results. For example, side imaging sonar scans the water horizontally, providing a wider field of view and revealing fish hiding in shallow areas.

Down imaging sonar scans vertically and offers a more detailed view of the underwater environment. The fish finder’s transducer emits a sonar wave in a cone shape, which helps to cover a larger area beneath the boat.

Sonar waves interact with various underwater surfaces differently. Hard surfaces, like rocks, reflect sound waves more effectively than soft bottoms, like silt or mud. This distinction can help anglers identify the type of bottom and possible fish habitats. It’s also important to be aware of the fish finder’s dead zone, or the area beneath the transducer where sonar waves cannot reach accurately due to surface clutter.

The fish finder’s display is crucial in presenting the collected data to the user. Flasher units display information using a rotating wheel of lights, while more advanced models use LCD screens to provide detailed images of the underwater environment.

Information gathered by the sonar technology is processed and converted into a visual representation, allowing the user to easily interpret the data.

how does a fish finder work

Types of Frequencies and Their Role

Fish finders work by emitting sound waves, or frequencies, into the water and interpreting the signals that are reflected back. The right frequency selection is essential for providing the most accurate and detailed images of the surrounding underwater environment.

Low frequencies (around 50 kHz) are typically used in deep waters and provide a larger coverage area with wider cones, making them suitable for detecting schools of fish or large structures. While these frequencies may not offer the highest resolution, they are often preferred in ice fishing and offshore environments due to their ability to penetrate deeper depths.

High frequencies (200 kHz or more) are more reliable for shallow waters, providing a narrow beam and a smaller cone. This allows for a more detailed view of the bottom structure, making it easier to identify individual fish, weed beds, and other underwater objects. However, their range is limited, and they struggle to reach greater depths.

Side imaging fish finders use additional frequencies to emit signals to the left and right of the device instead of just down. This technology allows anglers to get a broader view of the surrounding area, making it easier to identify structures or schools of fish. Side imaging works best in relatively shallow water, as the higher frequencies used for this technology lose their effectiveness in deeper waters.

The intensity of the reflected signals is determined by the size and composition of objects in the water. Schools of fish will typically produce strong signals as their air-filled swim bladders reflect sound waves efficiently. In contrast, soft objects such as weed beds may produce weaker or more diffuse signals.

Deeper Dive Into Cone Angles and Beams

Cone angles refer to the width of the sound waves emitted by the fish finder’s transducer. A wider cone angle provides more coverage of the underwater terrain, while a narrower cone angle offers greater detail. In most cases, fish finders have cone angles ranging between 15 and 20 degrees, suitable for a variety of water depths and conditions.

There are two main types of beams: narrow and wide. A narrow beam provides a more focused view of the bottom structure, making it ideal for detecting fish and details in deeper waters.

On the other hand, a wide beam offers a broader coverage that is useful for scanning large areas and shallow waters. It is important to note that a fish finder’s performance relies on the balance between these two types of beams.

When it comes to water depth, the beam’s width has a direct effect on the fish finder’s coverage. As the sound waves travel deeper into the water, the cone widens to cover a larger area of the bottom structure. However, this increased coverage comes at the cost of reduced sensitivity and detail. To maintain accuracy, a narrower beam can be utilized in conjunction with the wide beam to provide a more detailed view of the targeted area.

The right balance of cone angles and beam types is crucial for locating fish and identifying underwater structures and cover.

Some advanced fish finders even offer multiple beams that can be adjusted according to the user’s needs and preferences. This allows for a more versatile and efficient scanning process, as users are able to effectively cover a range of water depths and structures without the need for constant adjustments.

Using the GPS Functionality in Fish Finders

GPS, or Global Positioning System, is a satellite-based navigation system that enables users to pinpoint their exact location, track their movements, and even save specific coordinates for later use.

Modern GPS fish finders offer an array of features that simplify and elevate the fishing experience. By utilizing GPS coordinates, fish finders can create detailed maps of the fishing area.

These maps help anglers identify underwater structures, changes in depth, and other key factors that influence fish behavior. Having GPS data also allows them to mark productive fishing spots, making it easier to return to those locations in the future.

Another notable benefit of GPS fish finders is their ability to assist with navigation. Anglers, especially those venturing into unfamiliar waters, can leverage GPS data to plot their routes, keeping them on track and ensuring a safer excursion.

With the capability to record waypoints and utilize built-in mapping software, fish finder GPS units make it easier to navigate various water bodies, even in adverse weather or low visibility conditions.

In addition to these features, most GPS-enabled fish finders provide real-time weather updates and other relevant information that can be vital for a successful fishing trip. By having access to accurate, up-to-date data, anglers can make informed decisions about when and where to fish based on weather conditions, water temperature, and other factors known to affect fish activity.

To maximize the benefits of GPS functionality in fish finders, they should be set up and calibrated correctly. Many units allow users to customize settings, such as the display layout, map orientation, and depth alarms, to suit their preferences and fishing conditions.

By taking the time to familiarize themselves with these settings and configure them appropriately, anglers can optimize the usability and effectiveness of their GPS fish finder.

how does a fish finder work

Understanding the Reading and Display of Fish Finders

Fish finders typically have an LCD screen that shows a 2D sonar image of the underwater environment. The sonar system sends out sound waves, which bounce back when they encounter an object – like a fish or the bottom of the lake. The time it takes for the sound wave to be reflected back determines the distance to the object. The fish finder then processes this information and displays it as an easy-to-read image on the screen.

Arches are commonly seen on the display, representing fish swimming through the sonar beam. The size and shape of the arches give an indication of the fish’s size and orientation. If the arches are longer, it could mean that the fish is bigger or closer to the surface. A round arch indicates that the fish is horizontally oriented, while a slimmer shape may suggest a fish is swimming at an angle or hiding among underwater structures.

Some fish finders may include a flasher mode, which converts the traditional 2D display into a circular, compass-like view. The flasher shows the depth of an object with a bright segment on the outer edge of the circle. This mode is particularly useful for ice fishing, as it can detect fish even when the boat or angler is stationary.

Being able to effectively read your fish finder will significantly enhance your overall fishing experience.

Let’s Go Fishing

A fish finder is an essential tool for both professional and recreational anglers, providing valuable information on fish presence, water depth, and bottom structure. By utilizing sonar technology, it enables users to identify potential fishing spots and understand the underwater environment better.

Now that you’re more familiar with how fish finders work, be sure to check out our post on the 5 Best Kayak Fish Finders for Anglers!