Whether you fish for fun, as a sport, or for commercial purposes, a fish finder could make your fishing experience more predictable. It will help you to quickly and accurately scout the habitat. It also helps detect the precise location of fish underwater and its size. As a result, you will be able to decide which lures and fishing techniques to use.

There is a wide range of fish finders on the market. Although they may vary in shape, size, color, or features, their operation mode is fundamentally the same. Understanding how your fish finder works and how to use it will differentiate between a catch or miss.

How Do Fish Finders Work?

This section will look at the parts of a fish finder, sonar technology used in fish finders, and the basic fish finder operating mechanism.

Parts of a Fish Finder

A fish finder is made up of two parts: a display and a transducer. The display is placed on the boat to show images of the location of fish and their depths. The transducer produces a sound wave that is transmitted through the water and sends back a signal. Fish finders can give you a wide range of information, including:

  • Position of the object
  • Depth
  • Size of the object
  • Whether there is any object in between

The Fundamental Operating Mechanism of Fish Finders

Fish finders utilize sonar (Sound Navigation Ranging) technology to locate and determine the position of fish. In a fish finder, the transducer acts as the sonar device. It vibrates, producing sound waves that are sent down the water. If the sound wave hits an object, such as fish, coral reefs, or even the water bend, it is reflected back to the transducer.

The computerized system in the fish finder then calculates how far away the object depends on the amount of time the sound wave took to hit the object and then bounce back. The device can also approximate the size of the object depending on the strength of the reflected pulse.

Since sound waves travel at high speed, the transducer can send several waves in sequential order, a few seconds apart. The reflected pulse is transduced into an electrical signal displayed on the head unit/ display unit.

Understanding How the Sonar Technology In a Fish Finder Transducer Works

To better understand how a fish finder works, it is paramount to understand sonar technology in a fish finder works. Below are three characteristics of sonar signaling you need to understand to be able to interpret it correctly.

Sound Ranging Is Usually Conical Rather Than Straight

Since sound travels in waves, each wave pulse forms a conical shape that expands outwards. Most fish finders have a feature that allows you to control the wave range by changing the scanning frequency.

Whereas a wider beaming range is appropriate for scanning larger areas to get a general sense of the depth of your fishing area, it is not precise. It is best suited for shallower waters. On the other hand, a narrow beam scanning focuses on a smaller area but gives a more accurate reading. It is ideal for identifying the specific location of the fish in deep waters.

Sonar Devices Do Not Detect Objects Just Below the Water’s Surface

In Sound Navigation Ranging, the sound waves sent out by the transducer pass the surface nearby too fast for them to be reflected accurately. As a result, this region is referred to as the blind zone or surface clutter zone. If there is fish in this zone, you may not be able to detect it. Narrow beam scanning has a shorter clutter zone, while a wider beam has a larger clutter zone.

The Sound Wave Spreads Out

Since it is conical rather than straight, the sonar signal is narrowest just below the transducer and widest at the bottom.

How to Use a Fish Finder

Below are basic guidelines and tips for installing, configuring, and interpreting the information relayed by your fish finder.

Installing a Fish Finder

The first step for using a fish finder is ensuring that it is properly installed. Before beginning your setup, read through the manufacturer’s installation instructions. For some fish finders, you may need a professional to set it up. Note that it is not possible to use a fish finder without a boat.

Here are some fish finder installation tips:

  1. Ensure that the transducer is level. The best installation site is on or near the boat’s centerline. Experts advise using a transducer mounting board to ensure that the transducer is level.
  2. Do not mount the transducer near or behind turbulence causing structure such as the motor, engine, or strakes.
  3. Mount the transducer away from electrical devices that may cause electrical interference.
  4. Route the fish finder’s wires away from other wires.
  5. Coil the extra wires into a figure 8 pattern and then hold them together with a zip tie
  6. Ensure that the fish finder is plugged into an adequate source of power. Adhere to the power source guidelines indicated by the manufacturer. Do not plug the fish finder on the same power source as a trolling motor. Also, put a fuse between the power source and the unit.

Configuring a Fish Finder

After installing your fish finder, the next step is to configure the various settings, features, and functionalities.

Install or Update the Fish Finder Software

Like any other computer system, the fish finder is a computerized system that runs on software. You can easily update the software for most units by downloading the latest version to an SD card. Plug the SD card into the fish finder’s SD slot and turn on the system.

You will be provided with step-by-step, easy to follow prompts for updating or installing the fish finder’s software. It is important to register your fish finder on the manufacturer’s website so that you can be informed of new software updates as soon as they are available.


Frequency affects the scanning depth, width, and resolution. At lower frequencies, the scanning beam is wider and longer, which means scanning a wider and deeper area. However, the resolution is quite low, making the displayed images blurry.

Conversely, at higher frequencies, the scanning beam is narrow and shallow, but the resolution is high; therefore, you can clearly see the objects in the water. Higher frequencies are suitable for shallow waters, while lower frequencies work best for deep water.


Common fish finder modes include shallow water, deep water, ice fishing, slow trolling, saltwater, freshwater, etc.


Increasing sensitivity will enable you to see more fish; however, you will also see every detail in the water that may make your display too cluttered. The goal is to find a sensitivity range that offers a good view of the fish while not focusing on all other elements.

For most fish finders, you will need to switch off automatic mode so that you can manually the sensitivity to your desired level.

You should also configure the fish finder’s screen brightness, zoom range, color pallets, and scrolling speed and direction.

Interpreting What Is On the Fish Finder’s Display Screen

First, let’s address the scrolling display. Most fish finder digital display units show data scrolling from right to left, while some have an option for bottom to top scrolling. The scrolling is not an indication of fish movement. It is a sequential order of the information coming in.

The device is constantly transmitting new information as the transducer is constantly sending out new signals, with the incoming screen being a representation of the most recent information.

Here is how to interpret the various symbols and information presented on the display unit.

Identifying Fish

Most fish finders represent fish either as a fish icon or incorporate a fish-ID technology or fish arc. Depending on the scanning frequency and sensitivity, the icon or arc may be clear or blurry. Even half arcs and icons represent fish.

Determining the Size of the Fish

In sonar devices, longer arcs and icons do not mean that the fish is bigger. The length is an indication of the speed at which the fish is moving. The arc is longer if the fish are moving faster and shorter for slowly moving fish. The width of the arc or icon is the accurate indicator of the size of the fish. The thicker it is, the bigger the fish.

Interpreting Bottom Type and Hardness

The signal line thickness can interpret the type and hardness of the bottom surface. Thicker signal lines indicate that the surface is hard, while thinner or weaker signals indicate a softer surface. Signal line thickness is depicted by the color intensity and brightness.

In case there is a depression at the water floor, the line will be V-shaped when reeling or trolling the fish finder. The deeper the V shape, the deeper the surface. Note that when not trolling or reeling, the depressions are not identifiable as the bottom is presented by a straight line.

Depth of the Water

Typically, fish finders have an inbuilt depth finder that lets you know how deep the water is from the bottom of the roof to the water floor. The exact depth is usually displayed somewhere on the screen, either in meters or feet. In some fish finders, the depth finder feature also indicates the water temperature either below or next to the depth reading.

Identifying the Different Types of Underwater Structures

Aside from fish, the fish finder will also pick up images of other underwater structures such as rocks, pebbles, logs, and vegetation. Green spots or vertical lines often represent vegetation.


A fish finder takes the guesswork out of your fishing strategy. When you know how to use it properly, you will gather critical information such as the depth and temperature of the water, whether there is fish in the vicinity, the size and location of the fish, and also whether there are other objects in the water that may affect your fishing outcome. You’ll also want to consider how you’ll be using your fish finder – for example, you may be in need of one for your kayak instead of your boat.

If you’re looking for some fish finder recommendations, you can check these out: