You will be required to watch and maintain the main propeller shaft bearings. These bearings support and hold the propulsion shafting in align-ment. They are divided into two general groups: the main line shaft bearings (spring bearings), and the stern tube and strut bearings.

MAIN LINE SHAFT BEARINGS (SPRING BEARINGS)

The main line shaft bearings (spring bearings) are of the ring-oiled, babbitt-faced, spherical seat, shell type. These bearings (figure 4-3) are designed primarily to align themselves to support the weight of the shafting. In many of the older, low-powered ships, the bearings are not of the self-aligning type and consist only of bottom halves.

The upper half of each assembly consists only of a cap or cover (not in contact with the shaft) designed to protect the shaft journal from dirt. The spring bearings of all modern naval ships, however, are provided with both upper and lower self-aligning bearing halves.

The brass oiler rings (figure 4-3) hang loosely over the shaft journal and the lower bearing half, and are slowly drag fed around by the rotation of the shaft. The upper half of the bearing is

Figure 4-3.Main line shaft bearing.

grooved to accommodate the rings. As they glide through the reservoir of oil at the bottom, the rings carry some of the oil along to the top of the shaft journal.

On some steam driven ships, the most recent line shaft bearing design employs oiler discs instead of oiler rings for lubrication. At very low speeds (i.e., when the shaft is jacked for 24 hours while the turbines are cooling), the oil rings tend to slip and lubrication is sometimes inadequate. The oiler discs are clamped to propulsion shaft and have cavities at the periphery which carry oil to the top of the bearing regardless of the shaft speed.

Spring bearing temperatures and oil levels should be checked hourly while underway. At least once each year, the bearings should be inspected, clearances taken, and any defects corrected.