In addition to providing guided fishing trips, I also conduct on-the-water sonar training sessions for owners of Lowrance, Humminbird and Garmin sonar units.
Having done this for many years now, I have ordered the topics we cover in these training sessions in a logical way.
The first step is inspecting the entire sonar system so I know what I am dealing with and can verify that everything is in working order.
Assuming all is well with the first step, the next step is to level the sonar unit’s transducer. Since I have learned that this phrase ‘level the transducer’ means different things to different people, I will specify exactly what I mean by that.
To level the transducer means to ensure that the transducer’s bottom surface travels parallel to the lake’s bottom at the lowest in-gear speed the boat is capable of going.
Conversely, to level the transducer does not mean to make the angle of the transducer match the angle of the bottom of the boat’s hull. This is a mistake I see over and over again. In fact, a majority of the boats I work on, including newly delivered boats right from the factory or dealership, usually have the transducers positioned in this incorrect manner.
To enjoy maximum sonar performance, the transducer must be parallel to the lake’s bottom. Here is why ... think of a rubber ball; if you release the rubber ball and allow it to fall directly downward, it will strike the ground and bounce right back toward the point it was released from. But if you throw the ball downward at even a slight angle, the ball will not return to the point it was released from.
Sonar’s sound waves behave much the same way. If the sound is directed directly downward, the majority of that sound will bounce right back upward to the transducer. However, if that transducer is canted either forward or rearward, much of the returning signal is lost.
Several symptom can be observed which indicate a non-level transducer. The first is asymmetrical fish arches. Fish normally show as arches on ‘2D’ colored sonar. If the arch has a long left side and a short right side, the transducer is aimed too far forward. Likewise, if the arch has a long right side and a short left side, the transducer is aimed too far rearward.
Finally, poorly leveled transducers typically yield a fuzzy transition between the darker-colored water column and the lighter-colored bottom on down-imaging views, whereas that transition will appear clear and crisp when using a level transducer.
Leveling the transducer is a simple process and one that can be done in a matter of minutes. Working with a partner makes it even easier.
The first step is to obtain a short, approximately 10-inch long water level (bubble level) as would be used for carpentry, etc., and approximately 20 coins (I use quarters, but any coins will do).
Next, launch the boat and drive in a straight line going as slowly as the boat will go while constantly in gear. Choose a hard, flat spot on the boat, like the front or rear casting deck. As the boat is moving forward, place the level on that spot, in line with the keel, or midline, of the boat.
Most boats travel in a slightly nose-up attitude. This will cause the bubble in the level to go to the bow end of the level. Now, using the coins as shims, place as many coins under the stern (rear of boat) end of the level as necessary to cause the bubble to center itself in the level. Take note of both the exact position of the level and the exact number of coins used. Try to keep them in place while putting the boat back on the trailer. If this is not possible, just reposition the level and coins as precisely as you can after placing the boat back on the trailer.
Place the boat back on the trailer and (here is where the buddy comes in handy), drive slowly forward on minimally sloped terrain until the shimmed level once again reads perfectly level, then stop.
If a minor adjustment is needed, the trailer’s dolly wheel can be used to raise the nose of the boat. Take advantage of upward and downward sloping terrain to get the level’s bubble centered.
Once the shimmed level once again reads perfectly level, your boat is now on your trailer at the exact same attitude it was in while moving slowly forward in gear while on the water. If the sides of your boat have a scumline from dirt and debris, you may notice that this scumline is now roughly parallel to the ground, as well.
Now, take the level and place the top edge of it flush against the bottom face of the transducer and in-line with the keel (not side to side). If the bubble is not centered, your transducer is not correctly positioned. To correct this, simply loosen the hardware attaching the transducer to the bracket (do not unscrew the hardware connecting the bracket to the boat). Manually move the transducer until the level reads perfectly level (again, this is made easier with an assistant), and then tighten the hardware to fix the transducer into this new, correct position.
At this point it is wise to use either a scribe, permanent marker or automotive paint marker to make a witness mark on the bracket’s components which will reveal movement if, in the future, the transducer is bumped and moves from this desired position. Making this mark now will prevent having to re-do this whole procedure in the future.
Even inexpensive, entry-level sonars these days are feature-packed and, properly mounted and used, can be effective fish finding tools. Building on the weak foundation of a non-level transducer, however, will render even high-end units powerless to reveal all there is to see under the water’s surface.