To keep the HD 800kHz Si ability of your unit you will have to use the XTM-9-HDSi-180-T transducer which is the same as the standard transom mount XHS-9-HDSi-180-T transducer that new 898 unit. The difference between these two transducers is that the XHS version comes with hardware to mount it on the transom and the XTM version comes with hardware to mount it to a trolling motor. You can call the Humminbird Customer Resource folks at 1-800-633-1468 and talk to them about a transducer exchange. Another option you may wan to explore is to use your standard XHS-9-HDSi-180-T transducer with an aftermarket trolling motor adapter like the ones that Transducer Shield & Saver or Raptor make. The reason I mention these is that they not only adapt the transducer for trolling motor mounting but also help protect the transducer from those nasty rocks and stumps out there!