Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGMain Reduction Gear andPropulsion Turbine BearingsReduction gear bearings of the babbitt-linedsplit type are rigidly mounted and dowelled intothe bearing housings. These bearings are splitin halves, but the split is not always in a horizontalplane. On many pinion and bull gear bearings,the pressure is against the cap and notalways in a vertical direction. The bearingshells are so secured in the housing that thepoint of pressure on both ahead and astern operationis as nearly midway between the joint facesas practicable.Turbine bearings are pressure lubricated bymeans of the same forced-feed system that lubricatesthe reduction gear bearings.Main Thrust BearingsThe main thrust bearing, which is usuallylocated in the reduction gear casing, serves toabsorb the axial thrust transmitted through theshaft from the propeller.Kingsbury or pivoted segmental shoe thrustbearings of the type shown in figure 5-10 arecommonly used for main thrust bearings. Thistype of bearing consists of pivoted segments orshoes (usually six) against which the thrustcollar revolves. Ahead or astern axial motionof the shaft, to which the thrust collar is secured,is thereby restrained by the action of thethrust shoes against the thrust collar. Thesebearings operate on the principle that a wedgeshapedfilm of oil is more readily formed andmaintained than a flat film and that it can thereforecarry heavier loads for any given size.In a segmental pivoted-shoe thrust bearing,upper leveling plates upon which the shoes restand lower leveling plates equalize the thrustload among the shoes (fig. 5-11). The base ring,which supports the lower leveling plates, holdsthe plates in place and transmits the thrust onthe plates to the ship's structure. Shoe supports(hardened steel buttons or pivots) located betweenthe shoes and the upper leveling platesenable the shoe segments to assume the anglerequired to pivot the shoes against the upperleveling plates. Pins and dowels hold the upperand lower leveling plates in position, allowingample play between the base ring and the platesto ensure freedom of movement of the levelingplates. The base ring is kept from turning by itsnotched construction, which secures the ring toits housing.147.51XFigure 5-10.—Kingsbury pivoted-shoe thrustbearing.Main Line Shaft BearingsBearings which support the propulsion lineshafting and which are located inside the hullare called line shaft bearings, spring bearings,or line bearings. These bearings are of thering-oiled, babbitt-faced, spherical-seated,shell type. Figure 5-12 illustrates the arrangementof a line shaft bearing. The bearing isdesigned to align itself to support the weightof the shafting. The spring bearings of allmodern naval ships are provided with both upperand lower self-aligning bearing halves.Stern Tube and Strut BearingsThe stern tube is a steel tube built into theship's structure for the purpose of supportingand enclosing the propulsion shafting where itpierces the hull of the ship. The section of theshafting enclosed and supported by the sterntube is called the stern tube shaft. The propellershaft is supported at the stern by twobearings, one at each end of the stern tube.These bearings are called stern tube bearings .A packing gland known as the stern tube gland96