Lets say it is spring right after ice off, and I have fish belly to the bottom in 16ft of water. If I were to troll thru them with a floating Rap off a 3-way, how long should the dropper be?

8"

Here's how I decide....I put the three-way swivel right on the surface of the water and get up to trolling speed, watching to see how far below the surface the plug dives. Being that you want the sinker at least a few inches off the bottem, the plug should be diving a few inches deeper than the sinker. If you use a one foot dropper...just adjust the length of your leader to allow the plug to dive deeper or run shallower. Leader length plays a major role per the size/style of the lure.....generally that will be 8' to 12' long. Generally, shallow lipped lures work best off three-ways.

Happy New Year!