DublinCrappie,
First thing I would do is make sure that you have the latest software in your 787c2i unit. Currently that would be version 5.420. If you are not running the current software than update your unit (don’t forget to reset to factory defaults first) and try it again.

- What speeds is the boat moving at when you try and see these arches? There has to be movement between the fish and the transducer (boat) for the arch to form.

- Where is the transducer mounted?

- What water depths are you trying this at?

- What sonar beam(s) are you suing: 200kHz only, 83kHz only or 200/83kHz?

Post a Screen Snapshot of what you are seeing and also what menu settings you are using.