I'm a crappie newbie but I did a lot of trolling this summer. I used 1/16 oz feathered jigs w/minnows. They were on 4 lb line (thinner line will go deeper than thicker). I always kept my speed at less than 1mph, near .5 (gps). I also kept the boat in a circling pattern and mostly fished on the inside of the turn - thus making the jig go even slower.
Sometimes when the bite was slow, I would put a small bb on the line about three feet up from the jig. THat seemed to help sometimes. Usually my jig was about 6-8 feet deep over 12 feet of weeds. Sometimes on the inside turn the jig would go to the bottom.
More line out equals a deeper jig also. Bigger minnow will stay higher.