The quad beam transducer for our Side Imaging units is available in transom mount or trolling motor mount.  The transom mount quad beam transducer is part number XNT 9 QB 90 T.  The trolling motor mount quad beam transducer is part number XTM 9 QB 90 T.      Please note the transom mount quad beam transducer can be used for high speed readings in a 2D down looking sonar.  The quad beam transducer does not provide Side Imaging on the unit. The quad beam sonar coverage is not as much coverage as Side Imaging sonar, and the side imaging would thus be used in trolling applications over the quad beam for high speeds .  The quad beam transom mount transducer coverage is 2:1 (ex. 10 feet of water = 20 feet of sonar coverage).  This is just an added benefit that can be incorporated on the unit with this optional transducer.   In order to use both the Quad Beam and the SI transducer you would also need the TS3 transducer switch.