A turning propeller is electrically insulated from the hull by the lubricating oil film in the bearings. Electrical potential is generated between the shaft and the hull. As a result the cathodic protection of the ship will not protect the propeller. Electrical potential can cause currents in the bearings resulting in pitting of the bearing surfaces. Problems can be avoided if the shaft is earthed with a propeller shaft slip ring. This shaft earthing assembly comprises a pair of high silver content/graphite compund brushes mounted in a balanced brush holder, running on a copper slip ring with solid silver track.
