As the shaft rotates, friction between the rings and the shaft is enough to cause the rings to rotate with the shaft. The rings dip into the oil in the sump. Oil is retained on the inside diameter of the rings and is carried to the upper bearings by the rings. The action of the oil ring guides and the contact of the rings on the upper shaft cause the oil to be removed from the rings and to lubricate the bearings. The oil disc is attached to, and rotates with, the shaft.
Oil is removed from the disc by a scraper, located at the top of the bearing.
The oil then runs into a pocket at the top of the upper bearing shell. From here, the oil enters the bearing through drilled holes. Tests have shown that the disc delivers more oil at all speeds than the ring discussed earlier, especially at turning gear speeds. The disc is also more reliable than the ring. Some ships have line shaft bearings that are force lubricated by a pump.