Johns,
The unit does come packaged with a transom mount transducer.

It can be clamped to the trolling motor with an adapter. We sell an adapter for this but others are available from other companies or you could even make your own.

The Trolling Motor version of this same transducer is puck shaped and generally does better around rocks and weeds/grass but it works no better electrically or sonar-wise than the one you have.

We do have a transducer exchange policy but unfortunately it only applies to new unopened and unmounted transducers and their hardware.
http://www.humminbird.com/normal.asp?id=816
If you have already mounted the transducer I doubt that they will take in exchange but it won't hurt to check with them anyway.

If you do exchange your transducer or buy another one, please be aare that the 777c2 will also work with other transducers like the QuadraBeam.