How Does A Fish Finder Work?

A fish finder is a very useful device amongst seasoned anglers. I bet you heard about it too if you are interested in the sport and did some study. But what are a fish finder and fishfinder GPS combo? What does it do?

A fish finder is an electrical device. It uses sonar technology to locate and visually represent the elements and structures underwater. The main purpose of the device is to locate fish.

However, even a common fish finder can provide useful and interesting information about the seabed as well as submerged structures. The eye-catching part of a fish finder is its display unit. Obviously, right?

You are supposed to look at it a lot. Make a guess what it does. A more important part, on the other hand, is the transducer.

They can be of various sizes and shapes, But they all serve the same purpose – sending and receiving sound waves and converting the data into electrical signals.

Despite a wide range of look and functionality, the basic of all the fish finders is the same. They scan the surrounding water and collect information.

You can locate big fishes, and schools of baitfish, and find out the depth, structure, and sometimes temperature of the water too. Overall, a fish finder is inescapable for a pleasant and fruitful fishing trip.

That’s all simple and easy, but how does a fish finder work?

How Does A Fish Finder Work?

If you’ve gone on a fishing expedition with another angler, there’s a good chance you’ve seen a fish finder in action. The display unit is usually mounted on the hull of a boat or kayak, whereas the transducer is attached underneath and always kept submerged. You know the kayak fish finder works in the same way.

The transducer makes sound pulses that travel through the water. The sound pulses/waves then reach the seabed, and the seabed reflects it. The echoes travel back up and are picked up by the transducer, and thus the virtual image is made.

How Are The Fishes Located?

The transducer makes repeated pulses of sound. On its way down, when the sound wave is intercepted by a fish, a reflection is made. As I mentioned before, the reflection is then picked up by the transducer and marked as an object.

Other objects like rocks or trees or some other underwater things also make echoes the same way and are marked along with their depth.

What’s There On The Screen?

It’s a very simplified image of the underwater. It’s called raw data. After picking up echoes, the transducer converts them into electrical signals and sends them through a cord.

The signals are then shown on the screen as a moving image (raw data). It’s essentially an image that constantly moves from right to left, and new data is added on the right constantly.

Is There Simplification?

Yes, there is. A common fish finder usually displays raw data on the screen. An experienced angler has no issue reading them.

However, some advanced fish finders can differentiate between the echoes of different objects and show appropriate icons on display.

Those are easier to read, especially for newer users. However, they aren’t always accurate about their understanding and icon selection.

Does The Sound Frighten The Fishes?

No, it doesn’t. The sound waves that these machines make are usually either infrasonic or ultrasonic. Infrasonic sounds are sounds with such a low frequency that neither human nor fishes can hear them.

Thus, it doesn’t disturb the fishes at all. Ultrasonic sounds, on the other hand, are sounds with such a high frequency, that (again) they are beyond the hearing capability of the marine creatures.

How things work, those are technical stuff. I personally like to know the ins and outs of how things work. However, to use the machine properly, you’ll need to know how to use the machine. That’s far more important. Here’s how to read the reading properly.

How To Read A Fish Finder Properly

If you know some simple basics, reading a fish finder is very easy. The screen updates periodically. On each update, some new information is added on the right side of the screen, and the existing image shifts slightly on the left.

The very left bits get removed. From top to bottom of the screen is the depth, and from right to left is the time.

Read The Environment

the top portion of the screen is the level where the transducer is located. Not necessarily the water surface. And at the very bottom, you’ll see the irregular shaped seabed. Many fish finders will also show additional information such as the depth and temperature.

There’s usually a cluttered zone right at the top. It is caused by waves, air bubbles, debris, etc. This is like a blind zone. No real object (expectedly fish) will be detected or shown in this zone.

Beneath this, the visible zone begins. Any submerged floating object that passes through the sonic wave will make some amount of echo. This echo is responsible for making the object visible on the screen.

Understanding The Sound Pulse Structure

You should keep in mind that the sound wave sent and received by the transducer travels in a cone shape. Not in a straight line. Understanding this concept is important for understanding the location of a fish that is shown on the screen—time for science stuff.

A fish shown on the screen can be anywhere inside the width of the cone for that depth. The transducer is at the pointy top of the cone. And the sound wave travels down. If you know cones, you’ll easily understand that the cross-section of the cone becomes wider, the further away you are from the top.

All this implies that if you see a fish near the surface, the fish is more or less right beneath you. On the other hand, if you see a fish at greater depth, that means there’s a fish in the general area beneath you, not necessarily right beneath you.

Understanding The Echo

The echo made by the seabed is fairly easy to understand. Because it is pretty straightforward and boring. The interesting stuff is the kind that floats. A moving fish makes an arc on display. Because the transducer calculates the distance of an object from the probe.

When a fish is entering the scanning cone, it is the furthest away. The more it moves toward the center, the less the distance is, and at the center, it is closest. Again, the distance increases when the fish leaves the center and moves toward the edge of the cone. Thus, it makes an arc.

Understanding The Fish

A common misconception is to think that the length of the arc is proportional to the size of the fish. However, that is not the case. Remember, the image on the screen moves from right to left?

So, the horizontal length indicates the time. A longer horizontal line indicates that a fish is on the radar for quite some time.

How to Know the Size of the Fish Then?

That is shown as the thickness of the arc. The thicker the arc is, the bigger(hopefully) the fish is. Because a bigger object will reflect much more sound than a smaller object, making the arc thicker.

A concise but thick arc is a bigger fish compared to a long thin arc because the first fish is likely a fast-moving big fish that entered and escaped the sonic cone fast.

Another common appearance is a school of baitfish. Those are closely clustered numerous small objects. On display, they are shown as lots of clustered lines or dots baitfish sometimes attract other fishes.

Also, the presence and location of baitfish can give you much more information about the surrounding area and other vegetation as well as other creatures.

Final Thoughts

Overall, a fish finder is a simple machine based on simple science. But the result is magnificent. It is one of the most useful gadgets not only for the new anglers but also for the veterans.

Once you install one, you’ll no longer need to return empty-handed from a fishing trip (unless you happen to be extremely unlucky). All in all, the device is simple, easy to understand, and is one of the inescapable accessories of successful fishing.