Garmin GT21-THGarmin GT21 TH Perfect for coastal and offshore fishermen who want traditional sonar and CHIRP ClearV scanning sonar with a stainless steel stem, this thru hull mount transducer consistently displays clear and crisp fish arches with superior target separation as well as clear definition of structure below the boat. The CHIRP ClearV element has a power rating of 500 W and operating frequencies of 260 455 kHz. The traditional sonar has a power rating of