Yup, Kraken is absolutely right about the 525T-LTD/12 for use with the FCV585
This transducer is Dual-frequency and features 600 Watt of power. The 50 kHz low frequency side has 45° beam width for depth performance down to about 1200 ft. (353 meters). The 200 kHz frequency side has a12° beam width with a depth performance down to about 700' ft. (206 meters).
Also, be sure to select the right transducer in the FCV585's transducer set-up menu.