A fish-finding or depth-sounding transducer on the bottom of a trailer boat must run a gauntlet of bunks and rollers. Yet, you can minimize problems by choosing the right kind of transducer. Here are the three best types, with some tips on installing them to minimize trailer interference and maximize fish-finder performance.
Flush-Mount Through-Hull Transducers
Unlike conventional through-hull transducers that protrude well below the hull and might require a bulky fairing block, flush-mount through-hull transducers are virtually flat and far less likely to hang up on a trailer bunk or roller. These are available in bronze, plastic and stainless steel through-hull fittings with a 600- or 1,000-watt dual-frequency transducer element imbedded in the middle.
Some flush-mount transducers are designed to shoot perpendicular to the boat’s bottom (0 degrees) and so are best suited for boats with flat bottoms or an aft pad at the transom. For boats with V-bottoms, there are flush-mount transducers with tilted elements (12 and 20 degrees) that aim the signal straight down, even though the through-hull fitting is angled. These ’ducer types require at least a 2-inch-diameter hole for installation.
Though trailer interference is minimized, care should be taken to ensure that the transducer does not rest atop a bunk or roller when the boat is loaded.
Tip: To maximize fish-finder performance, avoid installing the transducer aft of other through-hulls, intakes or objects that might cause air bubbles to stream across the face of the transducer.
Transom-mount transducers are often the least expensive and easiest way to avoid trailer issues, because they’re usually aft of bunks, rollers or crossbars. Most transom-mount units come in 600-watt dual-frequency versions, as well as 1,000-watt CHIRP models.
The position, depth and angle of adjustment is critical to minimize interference from engine noise and water aeration. All transducers need to run in water free of turbulence. Also, transom-mounts are more prone to breakage from striking an object, though most have a bracket that lets the tranducer kick up.
Tip: Transom-mount transducers should be mounted on the starboard side on single outboard- or sterndrive-powered boats (with right-hand rotation props) or in between twin engines to help avoid interference caused by turbulent water.
While there is some fish-finder signal loss, shoot-through or in-hull transducers (available in both 600- and 1,000-watt versions) often prove an acceptable compromise for trailer issues.
Also, no holes need to be drilled. The installation is less difficult than in other methods and involves securing the face of the transducer to the inside of the boat. They come in a wide range of angles, allowing you to mount them on the angle of a V-hull. But they can only be used with solid fiberglass boats.
Tip: Test a selected area inside the boat by placing the transducer inside a water-filled plastic bag. Wet both the outside of the bag and the inside of the hull and hold the transducer as tight to the hull as possible. If your sounder registers down to the depth you fish, you are safe to install the transducer at this spot.