Modern boat fishing is no longer possible without an electronic assistant that allows you to look into the underwater world, hidden from the human eye. Many anglers perceive the echo sounder as a magical device that shows the fish in real time, but behind this miracle of technology is a clear physical principle that anyone who understands the basics of acoustics. Understanding how the device forms an image helps not just blindly trust the screen, but correctly interpret data, sifting out interference and finding the best points for fishing.
At the heart of any sonar is echolocation, a technique that nature gave dolphins and bats millions of years ago. It generates a sound pulse that propagates in the water, bounces off obstacles and returns back to the receiver. The time it takes to do this and the strength of the reflected signal are the raw data that the processor turns into a graphical picture on the display that we can understand. It is the accuracy of these measurements and the speed of processing that determines the quality of the final picture.
The fisherman needs to realize that the sonar does not see the fish in the usual visual sense, but only registers the presence of an object of a certain density. Sound wave. It reacts differently to air, water, hard bottom and soft tissue in a fish bladder, so to make good use of the device, it's important to understand the nuances of how the signal travels through different environments and how the sensitivity settings affect what you see on your boat screen.
Physical Basis of Echolocation: The Sound Wave Path
The scanning process begins with the fact that transducer It converts the electrical impulse from the head unit into mechanical vibrations, which is sound. It travels through the water at about 1,500 meters per second, which is much faster than in the air. When a wave meets an object with a density other than water, some of the energy is reflected back in its path. The harder the object, the stronger the reflection, which is why the bottom on the screen always looks the brightest and widest band.
The key parameter here is the frequency of radiation. Low frequencies (about 50 kHz) have a longer wavelength, allowing them to penetrate deeper and cover a wide cone, but they give a less detailed image. High frequencies (200 kHz and above) provide fine detailing of small objects and separation of layers, but their signal fades faster in water. Choosing the right scan frequency is a critical factor in determining whether you see an individual fish in a shoal or just a blurred spot.
There's also the concept of a dead zone right below the sensor, where the beam doesn't get into because of the way it's formed. And it's important to consider that sound in the water not only travels straight down, but also diverges to the sides, forming a cone. The angle of this cone determines the width of the area being covered: the wider the angle, the larger the area of the bottom you see, but the fewer details per unit of screen area.
Use dual-frequency sensors to simultaneously see the overall picture of the bottom at low frequency and detail objects at high frequency.
Transducer design: the heart of the system
The transducer, often referred to simply as the sensor, is the most important element of the entire system, because it is responsible for the quality of the incoming and outgoing signal. Inside the case of this device are piezoceramic elements that perform the energy conversion. The build quality, the housing material and the way the signal is attached directly affect how clean the signal will be received for processing.
There are several types of sensor attachment, each with its own specific features: PVC boats most often use transom mounts or special protective baskets that are attached to the cylinder. Metal boats require the installation of sensors through the hull or the use of special remote brackets to avoid metal interference. Incorrect installation can completely negate the capabilities of even the most expensive sonar.
There may be one or more crystals inside the sensor, and single-chip models alternate between radiation and reception, which creates a small delay. CHIRPThey can emit a continuous signal over a wide range of frequencies, which greatly improves the resolution and allows you to distinguish objects that are very close to each other.
Signal processing: from echo to picture
Once the reflected signal is returned to the sensor, it is converted back into an electrical pulse and fed into the head unit of the device, and here comes a powerful processor that must filter out useful data from noise. Water is a heterogeneous medium, it floats suspensions, air bubbles, thermoclines, all of which create interference that must be removed to make the picture readable.
Modern algorithms, such as DSP (Digital Signal Processing)It can detect even very faint reflections from small fish that would have been lost in the noise of the bottom. The processor analyzes the shape of the echo: a hard bottom will give a sharp peak, soft silt will give a more gentle, and a fish with a swimming bladder will give a characteristic arc or point. It is mathematical processing that allows the device to draw on the screen arcs (arcs), which anglers used to think of the image of a fish.
It's important to understand that the image on the screen is not an instant picture, but the result of the accumulation of data over a certain period of time. Scrolling speed (diagram speed) should be synchronized with the speed of the boat. If the boat is standing and the scrolling is fast, you will see vertical stripes. If the boat is swimming fast and the scrolling is slow, the image of the fish will stretch and lose shape.
⚠️ Warning: When driving at high speed, be sure to increase the speed of scrolling the screen in the sonar settings, otherwise the image of the bottom and fish will become unreadable and blurred.
Data Interpretation: What We See on Screen
The ability to read sounder comes with experience, but the basic principles everyone should know. The bottom is displayed by the lowest colored band, the color of which depends on the chosen palette and the density of the soil. Above the bottom you can see various objects. The fish is most often displayed as an arc. This is because when the boat swims above the fish, the distance to it first decreases, then becomes minimal (the fish in the center of the cone), and then increases again. The sounder draws this change in distance as an arc.
But it's not always a fish that's drawn in an arc. If the boat is anchored or moving very slowly, and the fish goes through the cone quickly, you'll see just a vertical line or a dot. It's also affected by sensitivity (Gain). Too high sensitivity will add a lot of "junk" and noise to the screen, too low will hide small fish. The optimal setting is a balance where you can see the structure of the bottom and the individual goals, but the screen is not full of chaotic dots.
The thermoclin is another important object that you can see on the screen, and it's a very high-temperature water layer that often looks like a thin line that separates the water into two layers. Fish often stand above or below the thermoclin because it concentrates oxygen and plankton. Understanding the structure of the water column helps predict where the predator will stand at a particular time of the day.
Why is the fish not always visible?
A fish may not be visible if it is in the “dead zone” under the sensor, if it is too shallow for the selected frequency, or if its swim bladder is compressed at great depth and does not reflect the signal.
Scanning technologies: DownVision and SideVision
Traditional 2D sonar shows what's directly under the boat. DownVision (view down) and SideVision They use high-frequency beams to create a detailed image that looks like aerial photography, and these technologies allow you to see not only the presence of fish, but also the structure of the bottom: driftwood, rocks, vegetation, sunken boats.
SideVision is particularly useful when looking for fish in large water areas, and it scans a strip up to 200-300 meters wide from the boat, and it allows you to quickly survey the eyebrows, dumps and vegetation boundaries without going directly over them.
In the parking lot, the picture will be distorted or disappear, since the image requires a constant change in the position of the sensor relative to the bottom. The speed of movement when using side view should not exceed 5-7 km / h, otherwise the picture will lose detail.
| Parameter | 2D Echoer | DownVision | SideVision |
|---|---|---|---|
| Review | Cone under the boat | Narrow lane under the boat | Wide lane to the sides |
| Details | Low/Medium | High. | High. |
| Max. Depth. | Large (up to 300m+) | Medium (up to 90m) | Medium (up to 90m) |
| Best application | Determination of depth and availability of fish | Search for the structure of the bottom and fish | Quick search in large areas |
Practical tips for setting up and using
To get the most out of your device, you need to adjust it to the right fishing conditions. Auto mode often works well, but in difficult conditions it can be wrong. Manual sensitivity setting (Gain) allows you to remove unnecessary noise from the suspension in the water or, conversely, add sensitivity when fishing at great depths.
The Refresh Rate also plays a role, and if you're actively fishing in a plumb or jig in the course, when the boat is constantly shifting, the high refresh rate will give you a smoother, more intuitive picture, and if you use a trolling sonar, you can lower the frequency to see a longer stretch of history.
☑️ Checking before getting on the water
⚠️ Warning: When you install the sensor on a transom, make sure that the front edge of the sensor is below the back edge, which will prevent air capture and the appearance of "noise candles" on the screen when moving.
Frequent mistakes of beginners when working with a sonar
One of the most common mistakes is to expect a sonar to show a fish in real time just as it bites. In fact, the sonar tells a story: you see a fish when it's already under the boat, so you have to throw the gear just ahead of the point where you saw the fish on the screen, given the speed of the boat and the depth.
Another mistake is ignoring the calibration of the speed of sound, because in salt water, sound travels faster than in fresh water, and if you move from river to sea (or vice versa) and you don't change the settings, the depth readings can be wrong, and many people forget to clean the sensor of algae and dirt, which drastically reduces the signal quality.
Don't just rely on one frequency. Experiment with switching between 50 kHz and 200 kHz (or other available bands). Sometimes large fish are only visible at low frequencies, and small feedbases are only visible at high frequencies. Combining data from different frequencies gives a complete picture of what's going on underwater.
The main secret of success is not just to look at the screen, but to analyze changes in the topography and structure of the bottom, since the fish is always tied to certain anomalies of the terrain.
Why does the sonar show arcs and not dots?
The arc is formed by the change in distance to the fish as the boat passes over it. When the fish is at the edge of the cone beam, the distance to it is maximum. As the boat approaches, the distance decreases, reaching a minimum when the fish is directly under the sensor, and increases again when the boat moves away. The sonar captures these changes in distance and draws them as an arc.
Does the color of the fish affect the sounder display?
No, the color of the fish doesn't matter to the sonar. The device only responds to the density of the object and the presence of a swimming bladder that reflects the sound wave. The black pike and the white pike will appear on the screen the same as long as they are at the same depth and are the same size.
Can I use a sounder in winter from ice?
Yes, but with limitations, the sensor must be in contact with water, it can be lowered into the hole, but in extreme cold, the battery can run faster, and the screen of some models can run slower, and it is also important to prevent the sensor from freezing.
What is Noise Reduction and when to turn it on?
Noise suppression is a filter that removes weak signals as interference, and should be turned on when there is a lot of suspension, algae or air bubbles in the water that create porridge on the screen, but too much noise cancellation can hide small fish, so use it carefully.
Why do you see vertical stripes on the screen?
Vertical stripes most often mean that the boat is standing still and the sensitivity is high, or the sensor is dangling on the surface, capturing air. If the boat moves and the stripes remain, perhaps the sensor is installed incorrectly and bubbly, or the simulation mode is on.