After so many trials and improvements on the pivot hole of the keel I finally decided to add two washers , one on each side of the keel at the pivot bolt level ...that should help prevent the keel from swinging sideways from starboar to port, and pendulum swinging. need advices for the material to use , of course weaker than fiberglass ( walls of the casing ) ..teflon nylon rubber ???and dimensions 4 inches diameter and quarter inch thickness ?????