Humminbird XFM 9 20 Plastic Flush-Mount Thru-Hull Transducer Thru-hull, flush-mount transducer, works with thinner hulls, while internal, steel sleeve provides extra reinforcement Dual-beam, with 20-, and 60-degree beam angles and operating frequencies of 200 kHz and 83 kHz Not recommended for trailered boats, and professional installation recommended Compatible with many of Humminbird's Piranha, Matrix and numbered series sonar systems Doesn't require a fairing block, and is backed by manufacturer's one-year limited warranty