marking a lot of fish helps to locate them but I've also had great luck when not marking a lot. but enough to keep me fishing. if you are marking fish then you have to dial in speed and depth to set your riggers. eyes feed best when going up a little to get the bait. with spoons and cranks, I've had better luck running as close to 2.8 as possible. for harnesses, I have done better at 1.6 on days. but most of the time I run a little faster at 1.8 to 2.0 when trolling the summer months.

as for depth with cranks, it's more of a guessing game. you want the lure at or just above the fish. you have to guess what depth the crank gets plus the depth of the rigger. if you're below the fish you may catch a few but you may not catch anything. I like to err on the shallow side and then drop the weights a little at a time until I find the sweet spot. but more times than not I'm usually good on depth when I start. shallow divers will dive much less than deep divers with much guesswork. in water less than 40' I don't allow for any blowback and allow for the dive of the lure. if I mark fish at 30' I set my rigger about 22; to start. this should put a shallow diver just above the fish.