i just bought a new to me bass boat. it is equipped with a hummingbird 798 ci hd with side imaging and gps at the console. and hummingbird 571 hd down imaging at the trolling motor. I have crappie fished most of my life but new to the depth finder world. I just want to find the structure and the shad. if I find that the fish will be there. anybody have these units? they good units?