I just purchased a boat with an Edson destroyer wheel. I'm new to all this, but the knob is missing from the center of the wheel - there's a nut that keeps coming loose, which makes the wheel wobble, but I'm sure there is supposed to be a knob that I can tighten by hand on the hub, I'm just not sure whether there's more to it than that. I haven't found a schematic of that part of the wheel on Edson's site, and am wondering what I need to do the repair.