Depth remains one of the most key variables in trolling, I don`t use charts just trial and error. Find a clean(no debris) point, underwater island,etc,on your locator, run over it with a gps (I use Lowrance h20) marking a track at what ever depth you choose. Put on your favorite crank and run the track varying speed and amount of line out until the crank just bumps. You may have to change crank sizes (series) to get the right depth. Write down your findings, example a Norman middle n will run a maximum of 16` no matter how much line (12lb.) I let out or speed I go. If you do not have a gps bouy markers can be used. Makes it a bit harder, but that is what I used for years. Hope this helps. PM me if you have any questionsI can help you with. possum1