How Does a Fish Finder Work and Other Basic Facts

By Richard | Fishing Advice

how does a fish finder work
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Fishing or sometimes called angling, is part of a water sport where fishers or anglers try to catch fresh or saltwater fish.

A typical angler would usually have fishing rods, a variety of fishing lines, and hooks as part of their fishing arsenal.

Though the market abounds with a variety of fishing gear for all types of fishing styles, some anglers still opt to use a fish finder.

You may be wondering how does a fish finder work, and does it help in increasing your catch?

Let’s check out this device and understand its function.

Fish Finder History

The first fish finder was commercialized in 1948 when two Japanese brothers developed this fish detecting device after several testings and modifications.

The Furuno brothers have a modest marine electrical company found at a small port in Nagasaki, Japan.

Their invention was a simple device that used a unique recording paper to document the things found underwater.

It’s a simple device that operates using a power switch, a search range, and sensitivity adjustment selectors.

The introduction of this fish detecting device paved the way for the scientific way of fishing in addition to the traditional method anglers do.

How Does a Fish Finder Work

For some anglers, having the typical fishing gear and accessories is not enough to locate and catch a fish; thus, using a fish finder is helpful.

A fish finder is a sound navigation and ranging device or SONAR that works by transmitting waves and waiting for an echo.

It helps locate schools of fish since it provides vital underwater information like how deep the water is before you hit the seabed and how the fish are distributed underwater.

The waves are directly sent down to the water from underneath the boat, where the fish finder is installed.

Using a fish finder allows the anglers to see what is under their boats through graphic representation and helps them identify the fish.

Types of Fish Finders

The use of fish finders every time fishers go out to the water has become necessary, increasing its demand; hence, increasing production.

Currently, there are three significant types of fish finders presently available in the market today, and they are:

1. DownScan Fish Finder

DownScan fish finders are getting popular among anglers since they are one of the most affordable among other fish finding devices in the market.

They offer a photorealistic view of what is directly under the boat.

This type of fish finder is suitable for small boats since it can only provide you with a short and narrow detection range in shallow and small inland lakes.

However, it can give you an almost lifelike picture and description of what you will find underwater.

On the other hand, the fish is only shown when the position is excellent, and the situation warrants it.

A fast-moving fish will not be recognized as well as the hardness of the soil underneath.

2. 2D Fish Finder

A 2D fish finder device is the traditional type familiar to most anglers and has a black-and-white or colored display that continually moves from right to left.

It employs a cone-shaped beam to interpret what is in the water within the covered column.

The coverage of the cone depends on the set frequency where higher frequencies produce a full cone, whereas lower frequencies have better and more precise details.

It can accurately display the hardness of the soil, its rough texture, and the fish underneath while you are out fishing.

Although you will not see graphic images on the screen, you can recognize the representations through constant practice.

3. SideScan Fish Finder

Using a side imaging device or a side scan fish finder gives you the option to scan larger areas and search for fish-filled areas of waters.

It can give you perfect quality images with an adjustable coverage area under your boat, which can range from one meter up to 30 meters wide.

No matter how extensive the coverage is, the fish finder will provide you with almost lifelike images.

This kind of device is perfect for fishing in open waters or large lakes with its wide range of capacity.

The only downside to a side scan fish finder is its high price range as compared to the other two devices.

Fish Finder Installation

You should properly install our device if you want to catch more fish each time you go on a fishing trip.

Below is an easy and straightforward installation process that you can follow.

1. Find the Mounting Spot

Locate the perfect place in the hull where you can mount the transducer, an electrical device that can transform one energy to another.

It is crucial that you install the transducer correctly and on the right spot for it to work and provide the correct information.

Choose a spot that is always submerged in water because the transducer always needs to be in the water.

If you intend to mount it near the propeller, make sure that there’s a minimum space of 15 inches between them to lessen the interference in the reading.

The transducer should be fixed and must not move every time the boat does.

how does a fish finder work

2. Test the Wires

Test the wires from the transducer to the batteries before mounting it on the boat to ensure that it is working correctly.

If the wires are too long, you can either clamp or tie it up securely to the fish finder using plastic ties.

The transducer wires should be far from the engine’s wire strap to avoid performance discrepancies from the fish finder.

3. Mount the Transducer

Once you have chosen to install the transducer, put a plastic block underneath and drill holes into it.

Put a silicone sealant around the drilled holes to keep the water from leaking.

4. Run the Wires

When it’s time to run the wires, you can run them above the transom or drill a hole through the transom that is way above the waterline.

Ensure that the wires are held in place by a clamp or a plastic tie every 15 inches intervals then connect them from the batteries to the fish finder.

Keep in mind that the black wire is negative, and the red wire is positive when connecting it to your power source and keeping the fuse attached to prevent damage to the device in case of a power surge.

5. Mount the Fish Finder

The last step is to mount the fish finder on the dashboard by marking the spot with a pen before cutting to ensure that you have the right size for the hole.


1. How Does a Fish Finder Transducer Work?

Before we go to how a fish finder transducer works, let us first try to understand what it is.

A transducer is the core of your fish finder that converts the electric pulse to acoustic energy or sound wave.

When the transducer transmits the sound waves and receives its echo, the fish finder can interpret what can be found under the water.

Now, how does a fish finder transducer function? A transducer will receive a series of high voltage electrical waves from the fish finder, which will then be converted into sounds by the sensor.

The sound will travel as pressure waves into the water, and when it hits an object, the waves will go back like an echo.

The transducer will receive the echo converting it back to electrical energy, where the fish finder translates it into an image displayed on the screen that will be relevant to the user.

2. Do Fish Finders Really Help?

Some say that you will only waste money on fish finders and that it is unnecessary to have one if you want to catch a fish.

Here are some reasons, even the most basic model of a fish finder is useful and worth using:

  • A fish finder is an excellent help in locating your bait that is left suspended in the water column so that you can bring it to the right spot.
  • Using a fish finder to target a particular fish will let you discover structures or flat areas, especially in an unfamiliar area.
  •  Fishfinders will also give you the information on how deep the bottom is, aside from what you can find underneath.
  • The device will let you observe the fish underneath, especially if you are out in the open water, allowing you to bring home a big catch.
  • Some devices have convenient GPS options, so you can take note of the place where you found plenty of fish species to catch and smoothly go back to the same spot at any time.

3. How Do You Read a Fish Finder?

Reading a fish finder will not be simple at first, but learning how to do it correctly is critical to the success of your fishing expedition.

All types of fish finder devices support either colored or grayscale display depending on the device’s model.

Hard and heavy objects produce a louder echo and a darker display on your fish finder screens.

The darkest object that will appear on your display will always be either the seabed or the bottom of the water.

Some tools, such as Fish-ID technology, will translate the necessary data into an easy-to-understand interface.

Some newer device models would even show various icons for rocks, plants, and schools of fish.

However, there are instances wherein a particular symbol is detecting a different object, showing inaccuracy.

Some fish finders are more accurate but will only display a series of arches and lines which need to be understood by the user.

For these kinds of devices, understanding the width of the arch is essential since it serves as a clue if it’s a fish or not.

Once you learn how to interpret the symbols displayed on your screens, you can be sure of a successful fishing trip every time.

Essential Factors to Keep in Mind

1. Sonar or fishfinder scan in cones and not lines.

All kinds of fishfinders survey the waters in cones and not just the things found directly under the boat.

Depending on your set frequency, the things appearing on your screen are objects found inside the coverage of the cone.

Fishfinders with wide beaming angles can scan large areas, providing the depth and bottom structure information but also lesser details and accuracy.

Extensive beam scanning is perfect for shallow waters since the coverage is broader. This narrow beam scan with smaller coverage but with accurate pictures.

When hunting for fish, try using the full beam to search for the fish's location, then use the narrow beam and explore the area to get the exact spot of the fish.

When looking for structures and other features, it is better to use the narrow beam to reduce the dead zone display on your screen.

2. Movement on the screen does not mean lots of fish.

Some anglers get confused and excited when they see a lot of movements on the screen, which are just the continuous flow of sound pulses from the device.

The best thing an angler can do to avoid confusion when looking for fish is to use the vertical flasher display, which is a live display on the right side of the screen that shows the actual scenario underwater.

3. Thicker lines and second echos mean hard bottoms.

Aside from the appearance of the bottom structure, the fish finder device can also tell if the base is hard.

If you want to be good at understanding why fish are at a specific spot, analyze the association of the fish on how soft or hard the bottom is.

4. Keep an eye on arches, and you will find fish.

Learning how to read raw data from your fish finders will help you to identify the fish and its size accurately through arches that will show on your display.

When practicing how to analyze raw data, always think vertical and keep an eye on half and thick arches since they usually indicate fish.


Learning how does a fish finder work will significantly benefit anglers since it will help them discover fish quickly, ensuring a bigger catch.

It may be intimidating at first, but constant practice will help you master the technique of analyzing the display.

Using a fish finder and partnering it with the best rod and reel combo will give you lots of fun while out in the water!

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