The arrival of a sonar boat marks the transition of fishing from the category of "guess where the bite" to the category of technologically advanced search of trophies. sounder It becomes the tool that turns chaotic movements into purposeful exploration of the bottom, and without it, you're essentially blind underwater, relying on experience and luck.
The market today offers hundreds of models, from simple "beeper" to complex cartplotters with side scanning. It is critical for a motorboat owner not just to buy an expensive gadget, but to understand how it works in conjunction with the engine and the propeller. Wrong choice or installation can reduce the efficiency of the device to zero, turning the screen into a useless picture with interference.
In this article, we will discuss the key aspects of choosing a sonar for a small-sized motorized boat, you will learn why frequency matters, how to avoid cavitation noise and where to place the sensor so that it shows a real picture of the underwater world, rather than artifacts from the operation of the propeller.
Principle of operation and main specifications of sonar
So any sonar is based on the principle of echolocation. It generates a sound pulse that travels through the water column, bounces off the bottom, fish or underwater objects and returns back to the sensor. The signal travel time is converted into distance, forming a profile of the bottom on the screen. For a motorboat, the key parameter is radiation.
Most budget and mid-range models operate at 83 kHz and 200 kHz. Low frequency (83 kHz) provides a wide viewing angle and deep penetration, which is useful when searching for fish at greater depths. High frequency (200 kHz) gives a more detailed picture, allowing you to distinguish individual schools of fish and the structure of the bottom, but at lower depths. The optimal solution for universal fishing on a motor boat is a two-frequency sensor that combines the advantages of both ranges.
The power of the emitter is also important, measured in watts (RMS) and determining how strong the signal can penetrate the water column and come back. For the shallow depths (up to 10-15 meters) that are characteristic of many water bodies that use light motor boats, excess power is not needed. However, if you plan to go to great depths or move at high speed, the power reserve will allow you to maintain a stable picture.
Why does the speed of the boat affect the sounder readings?
When a boat moves under the sensor, it creates a cavitation bubble, a zone of water and air mixture. Air bubbles effectively dissipate the sound signal, creating a noise screen on the screen. The higher the speed, the more bubbles, so high-speed search requires sensors with a special form factor or a device that minimizes vortices.
Types of sensors and how to attach them to the boat
The choice of how to install the sensor (traductor) depends on the design of your boat and the type of engine. A mistake at this stage can lead to constant interference or even the loss of expensive equipment. There are three main ways of mounting, each of which has its advantages and disadvantages for the owner of a motorboat.
The first and most common option is transom-holdingThe sensor is mounted on a special bracket, which in turn is attached to the trunk of the boat. It is a versatile solution suitable for most aluminum and plastic boats. The bracket allows you to adjust the depth of immersion and the angle of inclination, which is critical for tuning.
The second option is a cut-in sensor that is mounted directly into the hull of the boat (through the side), which provides the best signal quality, since there are no barriers between the sensor and the water, such as air or transom plastic, but the installation requires drilling the hull, which is not always acceptable, especially for PVC boats or aluminum "kazak" with a thin bottom.
The third option is a sensor that is mounted on the engine's lower unit, and it's a specific solution that's becoming popular because of its simplicity, and it's placed on the lower leg of the motor.
- 🛶 transom: easy to remove for the winter, versatile, but can cause interference at high speeds.
- ⚓ Cutting: perfect picture, no interference from the screw, but requires complex installation and sealing.
- 🔧 On the motor: ease of installation, the sensor is always in water, but there is a risk of damage to underwater obstacles.
☑️ Check before installing the sensor
The problem of interference and the effect of the motor on the sounder
The motor boat is a source of constant vibrations and hydrodynamic noise. The engine running, the rotating screw and the movement of the hull create cavitation. The air bubbles that enter the range of the sensor completely block the ultrasonic signal. On the screen, it looks like chaotic stripes or the complete disappearance of the bottom.
To minimize the impact of the motor, you need to position the sensor correctly. When transom fastening, the sensor must be lowered below the keel line (if any) and be in an area where the water flow is laminar, not turbulent. Often helps shift the sensor closer to the diametric axis of the boat or, conversely, closer to the board, depending on the design of the transom.
⚠️ Warning: Never install the sensor directly in front of the engine cooling system's water intakes or near drainage plugs. The surges of water create powerful vortices that make sonar reading impossible.
The boat's electrical system can also be a source of interference, and hinged motors, especially two-stroke motors, generate strong electromagnetic fields, and sonar power wires that run alongside ignition wires or tachometers can catch tips, use shielded cables, and try to spread the wiring as far away as possible from the sources of electrical noise.
Comparison of popular sonar models for small craft
When choosing a particular model, you should pay attention not only to the brand, but also to the functionality necessary for your boat. The market is divided into simple sonars (depth and fish only) and cartplotters ( sonar + GPS + maps). For a motorboat, having a GPS tracker is often more important than ultra-high-resolution screen, as it allows you to return to catchy points.
Below is a comparative table of specifications typical of the different classes of devices available on the market:
| Characterization | Budget echoer | Middle Class (GPS) | Top Segment (SideScan) |
|---|---|---|---|
| Screen resolution | 240x320 px | 480x272 px | 800x480 px and higher |
| Frequency | One (200 kHz) | Two (83/200 kHz) | CHIRP + DownScan |
| GPS module | No. | Built-in | Built-in + GLONASS |
| Price (probational) | Low. | Medium | High. |
Entry-level models are great at controlling depth and finding large shoals. Lowrance Hook2 or Garmin Striker The mid-range segment already offers CHIRP (compressed pulse) technology, which greatly improves target separation, which means that you will see not just a red arc, but a clear image of individual fish and bottom structures.
Flagship side-scan models (SideScan) turn the sonar into a radar-like image, showing a picture of the bottom on the sides of the boat at a distance of 100-200 meters. This allows you not to swim over the fish, but to find eyebrows, pits and sunken trees, swimming parallel to them.
Instructions for installation and initial setting
Installation of a sonar on a motorboat is a process that requires precision and consistency, starting with the choice of a head unit (display) that should be clearly visible, accessible to control, but not interfere with the control of the boat and not be subjected to direct impact of splashes. Mounting on a swivel bracket (Gimbal mount) is the standard.
The cable from the display to the sensor should be made with a margin of length, but without unnecessary cove, which can become entangled. The cable should not be overburdened, cut or expanded with twists, as this will violate the resistance of the line and lead to loss of signal. All connections should be securely insulated by thermal shrinkage and moisture-protective materials.
After physical installation and power connection (necessarily through the fuse!), you need to calibrate. Most modern devices have an "Auto" mode that tries to adjust the sensitivity and depth settings itself, but manual fine-tuning is often required to get a good picture.
The main parameters for manual setting:
- 🎚️ Sensitivity: Increase to noise, then decrease by 10 to 15 percent, which maximizes detail.
- 🌊 Colorline: Enable the mode where fish is displayed in color (usually yellow or red) and weak signals are shown in blue.
- ⚡ Scrolling Speed: For a fast boat, increase the speed of the scan so that the picture is not “lubricated”.
Use a shallow water test to adjust your sensitivity, stand above a flat bottom without fish, and adjust your sensitivity until the second bottom appears on the screen. Then turn down the value a little bit, which will be the perfect setting for finding active fish.
Frequent errors in operation and their elimination
Even the most expensive sonar will be useless if you make mistakes in operation. One of the most common problems is the wrong speed when searching. If you move too fast, you create a cavitation, and the sonar stops "seeing" the bottom. The optimal speed for scanning is 3-5 km / h. At this speed, the picture is stable and informative.
The second mistake is to ignore the angle of inclination of the sensor, so if the sensor is not perpendicular to the surface of the water (when the boat is standing on a flat ground), the signal will reflect not to the bottom, but forward or backward, which will lead to loss of signal on the move or the appearance of artifacts. Adjust the angle of inclination so that the line of the bottom on the screen is smooth and clear.
⚠️ Warning: Do not leave the transom sensor lowered in water when the boat is moored or stored in water for a long time unattended.
And users often forget about calibrating the speed of sound, which depends on the temperature and salinity of the water. Although this is less critical for freshwater bodies, when switching from cold to warm water or when entering deltas with salt water, the depth readings can "swim away." Periodically check the sound sounder readings with known depths or a manual lot.
The key to successful echoerfishing is not just looking at the screen, but learning to interpret the fish's arches and bottom structure by matching them to the topography of the body of water. The echoer does not show the fish but the reflection of the swim bladder, and learning to read those signals comes with experience.
FAQ: Frequently asked questions
Can I use a sonar in winter if I leave the boat on the water?
Most household sonars have a working temperature range of up to -10...-20 °C, but lithium batteries lose capacity quickly in the cold. In addition, a sharp temperature difference when applied to heat can cause condensation inside the housing. If the ice is not thick, it is better to use winter sounders flashers, and summer protect.
Why does the sonar show "porridge" instead of the bottom?
It's probably in the cavitation zone, or it's overgrown with algae, and check the purity of the emitter and try to lower it deeper or move it away from the propeller jet, and check the sensitivity settings, and it's probably twisted to the maximum.
Do I need a GPS sonar if I know a pond?
Yes, even if you know a pond. GPS allows you to put points on specific driftwoods, pits or eyebrows where the peck was, and next time you can go back to exactly the same spot instead of looking for it by pumping, and the track feature will also help you find your way back in fog or unfamiliar terrain.
Is the sonar bad for fish?
No, the radiation output of household sonars is negligible and absolutely safe for ichthyofauna, because ultrasound frequencies don't affect fish behavior, they only react to the shadow of the boat, the noise of the motor and vibration, and the sonar only helps you find the place where the fish are already.