Garmin makes several different types of sonar and each requires a different type of transducer to work most efficiently. Matching the transducer to your device's sonar is very important. An in-hull transducer is installed inside a boat hull against the bottom and sends its signal through the hull. Transom transducers are attached to the back (transom) of a boat hull. Thru-hull transducers, as their name implies, are installed in a hole drilled thru the hull.