The AIRMAR P79 includes a plastic housing which is aligned to the centerline and secured inside the hull then filled with non-toxic coolant. The transducer is inserted into the housing and adjusted for the proper deadrise offset, insuring the beam is shooting straight down for maximum echo return. The coolant provides the best medium to transmit through the fiberglass and into the surrounding water. The major benefit of in-hull transducers is no protruding features on the exterior of the hull, making it the perfect choice for trailered or lifted boats. Designed for smaller boats up to 25 ft with solid core, fiberglass hulls.