Lowrance 3500C is the one your thinking of. Damn good piece of Kit. Our previos Boat was Lowrance equipped and proved V reliable , specced Blue "C" with lowrance 3500c and 52i sonar/GPS. been used wll over 150 hrs this year in all weathers and still going. Visit Lowrance.com and download emulators for the gear your intrested in. You can then sit and play with the thing on your PC
knew our well before it was fitted. Also Lowrance provide operating software update downloads,which are simplicity itself to upload to the unit.
Regards and happy hunting