Question about depth finders

[carolina-rig-01]

I am gonna partially answer your question and hope it steers you in the right direction, because I don't know for sure whether this relates to the 578 or not.

With the side imaging units such as my 1198, you can get a Y cable and a through the hull transducer. The Y cable will connect to the side imaging transducer as well as the through the hull transducer. Then you can switch to the through the hull transducer when your on plane, because your side imaging transducer is mounted in such a way that it will be out of the water when the boat is on plane. Your side imaging won't work with this transducer, but you would probably get to use your 2D sonar, and certainly would get depth readings. I guess you just need to find out if they offer the same system for the 578.