YBR,
Keep in mind that the TM185HW 1kW Transom Mount Transducer Chirps at a range of 150kHz - 250kHz, while the TZT3 Internal Sounder Chirps in the range of: 40kHz - 225kHz.
The TM185HW will not provide any type of Bottom Discrimination Capability. It was not designed to have any type of Low Frequency Range. Bottom Discrimination requires sampling from both the High and Low Frequencies to determine what the bottom characteristics are. Mud, Rock, Sand, and Gravel all have a somewhat distinct return echo so in able to attain this you need both High & Low Frequencies giving you sampling of both these return echoes.
The TM185HW was not designed to do this. :noway
- Deep Blue