Installing a sonar on a transom is a classic solution that most water-engineers choose, but if you want to maximize accuracy at high speeds, you can install it directly on the surface. lower unit This arrangement of the sensor ensures that it is always in water, even in sharp maneuvers or in shallow waters where the transom emitter can "grab" air.
Many tech owners are afraid to drill holes in lower unit, and that's a perfectly normal reaction. epoxy This is a way to get the installation done without compromising the tightness of the case, and the key is to follow the surface preparation technology and not to skimp on materials, and in this article we will look at all the nuances of the process, from the choice of location to the final setting.
It should be noted immediately that connection to the motor often involves mechanical installation of the sensor, and not electrical integration with the ECU of the engine. battery The voltage of the on-board motor network can be unstable, so let's take a look at how to turn your motor into the perfect fishing platform.
Selection of location and preparation of lower unit
The first and most critical step is to determine the ideal mounting point, and the sensor should be in the clear water flow zone, away from the propeller, so that the cavitation bubbles don't distort the signal, which is usually the flat part of a lower unit, just above the anti-cavitation plate, but below the waterline when moving.
The surface of the chosen place should be perfectly smooth. If lower unit has ribs of stiffness or irregularity, it is better to choose another site or use special fairings. For aluminum engines, the process is easier, since metal is easier to process than composite alloys of modern times. Tohatsu or Yamaha.
Degreasing is a step that you can't rush. Any grain of sand or trace of oil will negate adhesion of the glue. Use acetone or specialized cleaners for plastic and metal. Make sure the room is dry and warm, otherwise the condensation on the metal will ruin all the work.
⚠️ Warning: Never drill through a lower unit unless you have industrial installation skills and are confident in the tightness of threaded joints. Pressurized water at 50 km/h will turn a microscopic gap into a fountain.
Technology of mounting the sensor on glue
The most common method is to stick the sensor together, using two-part epoxy adhesives or special high-strength polyurethane sealants, and it is important that the material is elastic after drying to compensate for the vibrations of the motor.
Apply glue or sealant not only to the sensor itself, but also to the prepared site of the lower unit, and when pressed, the surplus should protrude at the edges, forming a collar, which ensures that there are no air bubbles between the emitter and the housing, which is critical for the signal to pass.
The time to complete polymerization can be anywhere from 24 to 48 hours depending on the ambient temperature. Don't rush the motor into the water early. Lack of dry adhesive can detach under high-speed water pressure.
After installation, make sure that the cable is not tense and not rubbed against other structural elements. clap to fix the wire along the lower unit, leaving small loops to compensate for the vibration.
Electrical circuitry and interference protection
Although the sensor is physically on the motor, the sonar is powered by the boat's onboard network; direct connection to the engine generator is possible only through the stabilizer, since the voltage can jump from 12 to 14.5 volts and above. The standard scheme involves the output of the cable through the process hole in the lower unit (if provided by the manufacturer) or along the lower unit leg.
To protect electronics, be sure to use a fuse mounted in the plus wire as close to the power source as possible. The fuse value depends on the consumption of your sonar, usually 1-2 Ampere. Using a more powerful "automatic" can cause the board to burn when short circuit.
Pay special attention to shielding. The motor generates powerful electromagnetic fields, especially if it's a power shield. two-stroke Put the sonar cable away from the high-voltage ignition wires.
| Component | Function | Recommendation |
|---|---|---|
| Safety lock | Protection from the KZ | 2A, in thermal shrinkage |
| Power cable | Transfer of energy | Copper, section 0.75 mm2 |
| Thermosaur | Isolation. | Glue, glue-coated |
| Connectors | Connection | Waterproof, brass. |
Fighting Vibration and Cavitation
Vibration is the main enemy of accurate readings. Even microscopic vibrations of the sensor can break acoustic contact with water. If you notice a fish nuisance or chaotic stripes on the screen when you move, then the sensor vibrates.
To combat this phenomenon, use damping gaskets between the sensor and the housing, if the design allows, and a more rigid cable fixation also helps: the bolting wire acts as an antenna, transmitting vibrations to the emitter.
Cavitation often occurs when you're turning abruptly or on a wave, and the right angle of inclination of the sensor helps minimize this effect, and the surface of the sensor should be parallel to the bottom when the boat is moving, not statically.
⚠️ Warning: If you have chipped paint around the sensor after you install it on lower unit, it's a sign of cavitation erosion, change the angle of installation immediately, or raise the sensor higher, or the metal will start to break down.
Set up the sounder after installation
After physical installation, you need to configure the software part. From the sounder menu, select the type of sensor installed (83/200 kHz or 50/200 kHz), and the wrong choice will lead to a distortion of depth.
Adjust sensitivity. lower unit is usually cleaner, so you can set the sensitivity higher than the transom attachment, but too high will add to the noise.
Use the function ASIC or automatic noise reduction settings, if available in your model Garmin or LowranceThis will help cut off echoes from air bubbles that may still be entering the scanning area.
Service and seasonal storage
The sounder in the lower unit is aggressively exposed to saltwater, UV radiation and mechanical impacts on the algae. Regularly check the condition of the sealant. The appearance of cracks is a signal for immediate repair.
When conserving for the winter, be sure to remove the sensor if the design allows, or wash the lower unit thoroughly with fresh water. The salt, crystallized, can damage the radiator body or disrupt the tightness of the connection.
Check the integrity of the cable. Friction on a transom or other objects during the season can wipe the insulation. Use protective corrugated or spiral braids for additional protection of the wire.
Can I put a sensor on a painted lower unit?
Technically, you can if the paint is very strong (for example, factory coating), however, for maximum reliability, it is better to clean the stain to metal or smooth plastic so that the glue contacts directly with the material of the case, rather than with a layer of paint that can peel off.
Does the installation affect the engine guarantee?
lower unit drilling almost always voids the engine water warranty. Sticking the sensor can also raise questions for service providers if they think the mounting caused corrosion or damage, and be prepared for that risk.
Which glue is best for installation?
The most established two-component epoxy adhesives with titanium filler (for example, Devcon or ABRO) and specialized marine sealants based on polyurethane (3M 5200), although the latter dries for a very long time.
Why does the sounder show the "steps" of depth at speed?
This is a classic sign of cavitation, or air falling under the sensor, and when you put it on a lower unit, it often means that the sensor is set too low and it's raking water along with the propeller, or it's too high and it's grabbing air on the wave.