You will be required to monitor the operation of the propeller shaft bearings and to maintain them in good condition. These bearings support and hold the pro-pulsion shafting in alignment. Three kinds of bearings are used for a main propulsion shaft: LINE SHAFT BEARINGS (or SPRING BEARINGS), STERN TUBE BEARINGS, and STRUT BEARINGS. We will briefly discuss each of these bearings. Refer to figure 12-16, which illustrates the general location of the bearings on main shafting.

Line Shaft Bearings or Spring Bearings

Most of the line shaft bearings or spring bearings are the ring- or disc-oiled, babbitt-faced, spherical seat, or shell type. This type of

Figure 12-14.-Kingsbury pivoted-shoe thrust bearing.

Figure 12-15.-Diagrammatic arrangement of a typical thrust bearing.

Figure 12-16.-Main shafting.

Figure 12-17.-Main line shaft bearing (ring oiled).

Figure 12-18.-Line shaft bearing (disc oiled).

bearing (fig. 12-17) is designed primarily to align itself to support the weight of the shafting. The brass oiler rings, shown in figure 12-17, are a loose fit. The rings are retained in an axial position by guides or grooves in the outer bearing shell. 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 disc-oiled spring bearing (fig. 12-18) is basically the same as the ring-oil type except it uses an oil disc to lubricate the bearing. 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. (Fig. 12-19 shows the scraper arrangement .) 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.

Figure 12-19.-Disc-oiled line shaft bearing scraper arrangement.

You should check the line shaft bearing temperatures and oil levels at least once an hour. Inspection and maintenance should be done according to PMS requirements.