A ship is moved through the water by an axial thrust that is developed by the propeller and transmitted to the ships structure. This axial thrust is transmitted by the shaft through a thrust bearing which is located either at the forward end or at the after end of the main reduction bull gear or in the propeller line shafting aft of the gear. Pivoted-segmental shoe bearings (Kingsbury type) utilize a wedge-shaped film of oil in their opera-tion. The source of lubricating oil for thrust bearings depends on the location of the bearings. In some installations oil is provided by the same system which furnishes oil to the reduction gears. In other installations, a separate lubricating system is provided.

Kingsbury-type thrust bearings consist of a collar mounted on the shaft and revolving between one or more sets of babbitt-faced segmental shoes. The backs of these shoes rest against round hardened steel pivots which permit the shoes to assume a tilt and change their angle with respect to the shaft collar. Bearings in which the thrust is always exerted in the same direction are equipped with shoes on one side only, but since provision must be made in most marine applica-tions for thrust in two directions, it is more com-mon to find shoes on each side of the collar. The shoes are free to adjust themselves at an angle to the collar. Rotation of the shaft collar drags a film of oil into the space between the shoes and the collar, and as the oil film forms, the shoes adjust themselves to the angle most efficient for the load conditions and the oil viscosity.

Additional information on Kingsbury-type thrust bearings and other types of bearings is pro-vided in the NAVSHIPS Technical Manual, chapter 243. Detailed information on allowable tolerances and procedures for taking thrust bear-ing readings can be obtained from the manufac-turers technical manual. End play checking of a Kingsbury thrust bear-ing must always be done with the upper half of the housing solidly bolted down, otherwise the base rings may tilt and provide a false reading. Keep a record of the end play measurements and refer to them when checking the main thrust bearing. The normal wear of a pivoted shoe-type thrust bearing is negligible even with years of use. However, when a thrust bearing is new, there may be slight settling of the leveling plates. If you notice any increase in the end play, examine the thrust shoe surfaces, and make all necessary repairs.

In most cases, the main thrust bearing cap must be removed for inspection. The opening is of such size that it will permit the withdrawal of the pair of ahead and astern thrust shoes located in line with it.

CHECKING END PLAY WHILE RUNNING THE SHAFT.The simplest method of checking end play is to use a suitable measuring instrument on any accessible part of the propeller shaft while running the shaft slowly ahead and astern. This is normally done at the end of a run when the ship is maneuvering to approach the pier before the machinery and shaft are cold. Although the speeds should be slow to avoid adding deflections of bearing parts and housing to the actual end play, these speeds should be sufficient to overcome the rake of the shaft and to ensure that the full end play is actually taken up.

End play is measured with a dial indicator mounted on a rigid support close to any convenient coupling flange. Occasionally a shaft may have a shoulder turned on it for the sole purpose of applying a dial indicator. Make sure that the flange surface is free from paint, burrs, and rust spots. The flange surface should also be well oiled in order to prevent damage to the dial indicator.

JACKING ON THE SHAFT FLANGE.If it is not feasible to measure the end play of a shaft while running, your next choice is to jack the shaft fore and aft at some convenient main shaft flange. Use a dial indicator make certain that the shaft movement is free, and guard against overdoing the jacking force. The main difficulty associated with the use of the jacking methods is in finding suitable supports to ensure that no structural damage will be incurred when jacking is done against a main shaft flange coupling.