Interesting post. I downloaded the Navionics phone app and have found and marked many waypoints to try. Several have been productive. I can do that at home and then find on lake and save on DF. If my subscription was current I could just download to an SD card and update my DF but this works well also.
I had never heard of a freshwater Drum until I caught some on Lake Erie jigging for Walleye. Thought I had a monster Smallmouth or Walleye until I netted a 7# drum.
I've never seen one in our SC lakes.