PRINCIPLES OF NAVAL ENGINEERING 



Main Reduction Gear and 

 Propulsion Turbine Bearings 



Reduction gear bearings of the babbitt-lined 

 split type are rigidly mounted and dowelled into 

 the bearing housings. These bearings are split 

 in halves, but the split is not always in a hori- 

 zontal plane. On many pinion and bull gear bear- 

 ings, the pressure is against the cap and not 

 always in a vertical direction. The bearing 

 shells are so secured in the housing that the 

 point of pressure on both ahead and astern oper- 

 ation is as nearly midway between the joint faces 

 as practicable. 



Turbine bearings are pressure lubricated by 

 means of the same forced-feed system that lu- 

 bricates the reduction gear bearings. 



Main Thrust Bearings 



The main thrust bearing, which is usually 

 located in the reduction gear casing, serves to 

 absorb the axial thrust transmitted through the 

 shaft from the propeller. 



Kingsbury or pivoted segmental shoe thrust 

 bearings of the type shown in figure 5-10 are 

 commonly used for main thrust bearings. This 

 type of bearing consists of pivoted segments or 

 shoes (usually six) against which the thrust 

 collar revolves. Ahead or astern axial motion 

 of the shaft, to which the thrust collar is se- 

 cured, is thereby restrained by the action of the 

 thrust shoes against the thrust collar. These 

 bearings operate on the principle that a wedge- 

 shaped film of oil is more readily formed and 

 maintained than a flat film and that it can there- 

 fore carry heavier loads for any given size. 



In a segmental pivoted-shoe thrust bearing, 

 upper leveling plates upon which the shoes rest 

 and lower leveling plates equalize the thrust 

 load among the shoes (fig. 5-11). The base ring, 

 which supports the lower leveling plates, holds 

 the plates in place and transmits the thrust on 

 the plates to the ship's structure. Shoe supports 

 (hardened steel buttons or pivots) located be- 

 tween the shoes and the upper leveling plates 

 enable the shoe segments to assume the angle 

 required to pivot the shoes against the upper 

 leveling plates. Pins and dowels hold the upper 

 and lower leveling plates in position, allowing 

 ample play between the base ring and the plates 

 to ensure freedom of movement of the leveling 

 plates. The base ring is kept from turning by its 

 notched construction, which secures the ring to 

 its housing. 



147.51X 

 Figure 5-10.— Kingsbury pivoted-shoe thrust 

 bearing. 



Main Line Shaft Bearings 



Bearings which support the propulsion line 

 shafting and which are located inside the hull 

 are called line shaft bearings, spring bearings, 

 or line bearings. These bearings are of the 

 ring-oiled, babbitt-faced, spherical-seated, 

 shell type. Figure 5-12 illustrates the arrange- 

 ment of a line shaft bearing. The bearing is 

 designed to align itself to support the weight 

 of the shafting. The spring bearings of all 

 modern naval ships are provided with both upper 

 and lower self-aligning bearing halves. 



Stern Tube and Strut Bearings 



The stern tube is a steel tube built into the 

 ship's structure for the purpose of supporting 

 and enclosing the propulsion shafting where it 

 pierces the hull of the ship. The section of the 

 shafting enclosed and supported by the stern 

 tube is called the stern tube shaft. The pro- 

 peller shaft is supported at the stern by two 

 bearings, one at each end of the stern tube. 

 These bearings are called stern tube bearings . 

 A packing gland known as the stern tube gland 



96 



