Richard
Fishing crankbaits are a lot like any other style of crappie fishing...everybody has there on way of doing it that works best for them...and it can change from day to day depending on the mood of the fish. TNfisher gave a great explanation in his post. Things that I might add that may help...
1) Be patient with it and stick with it. you may not load the boat down with fish, but what you catch will be good ones.
2) 1.5-2mph is the standard...but don't be scared to go faster. sometimes faster is all it takes to trigger the bite...most of the time a reaction bite.
3) wiggle the boat while trolling. the stop and start of the crank will trigger the trailing fish to bite.
4) color matters. somedays they que in on a specific color and that is all they want. other days it doesn't matter about color. yesterday on Loudoun, they would only hit one color of bandit for us. I had three of that color and those three rods were the only rods that caught fish all morning. I am changing colors constantly. treat it just like you do pulling jigs in the spring. change colors and styles of cranks often.
5) don't be scared to troll where there is brush or stumps. if you hang, break it off and watch for your crank to float to the surface. 8 out of 10 times it will float up and I will circle around and pick it up.
6) location, location, location. keep looking until the depth finder is showing fish. creek channels, mouths of creeks, main river channel breaks, main river flats, just keep looking and searching until you find em.
7) sharp hooks are a must. without sharp hooks you will get bites and not hook up. or the fish will surface way behind he boat and shake his head one time and out will come the crank. I use gamagatsu and they do well.
8) I mostly use bandits, arkie 350's, wiggle warts, walley marshall crappie cranks, and shad raps....each has it better day...it just depends.
9) smaller line will get you deeper if necessary.
10) line counter reels will keep you at the same depth on every rod.
hope this helps.