Chapter 4—REDUCTION GEARS AND RELATED EQUIPMENTThe mechanical face seal is a ring made ofeither a hard synthetic or a carbon compound.This ring is held tightly against the seal ring bysprings mounted behind it.NOTE: More information on face-type sealsis available in manufactures technical manuals—(Crane Co., “Surface Ship, Seal Inc.“,“Submarine”).STRUT BEARINGSThe strut bearings, like the stern tube bear-ings, are equipped with composition bushingswhich are split longitudinally into two halves. Theouter surface of the bushing is machined withsteps to bear on matching landings in the bore ofthe strut.Since it is usually impracticable to use oil orgrease as a lubricant for underwater bearings,some other material must be employed for thatpurpose. Materials that become slippery when wetinclude natural or synthetic rubber; lignum vitae,a hard tropical wood with excellent wearingqualities;and laminated phenolic materialconsisting of layers of cotton fabric impregnatedand bonded with phenolic resin. Strips of thismaterial, as shown in view C of figure 4-5, arefitted inside the bearing. A rubber compositionis the type most used in modern installations.CONTROLLABLE PITCH PROPELLERSThis section will describe the major com-ponents and the principles of operation of the con-trollable reversible pitch (CRP) propeller (a partof the main propulsion system).COMPONENTS OF THE CRPPROPELLERMost ships that use CRP propellers use twoindependent units with their associatedmechanical, hydraulic, and electronic pitch con-trol mechanisms, plus all the required valves andseals. Some type ships require tubing and passagesfor the discharge of prairie air through each pro-peller blade. The CRP propellers form an integralpart of the ship’s two shaft main propulsionsystem. Figure 4-6 shows the major componentsof a single CRP propeller.Figure 4-6.—CRP Propeller Machinery.4-11
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