Kind of ancient history as I havent used mine for a while. I have 2 cannon manual downriggers for my boat. They worked well for suspended fish. I used to troll rapalas at various depths and did well on trout. I'd let out plenty of line to get away from the boat and then clip it to the down rigger and drop it to whatever depth, even if only 10 or 15 feet. It worked really well to get fish on light line without a bunch of weights on it.
They don't work all that well for bottom hugging fish like mackinaw. Ok, but not great. Let them down till they bounce bottom, up a crank or so to not foul on bottom, drop it down to make sure your on the bottom, crank it up, repeat endlessly.
You have to watch for slack when the line comes out of the clip, I tried to use a lot of line behind the clip if fishing shallow, and closer to the clip when fishing deep. Think triangles and try to keep the hypotenuse as similar to one leg or the other as you can.