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1、,Lesson 25,Shafting(轴系) And Propeller,The transmission system(传动系统) on a ship transmits power from the engine to the propeller.,The thrust from the propeller is transferred to the ship through the transmission system.,The different items in the system include the thrust shaft(推力轴), one or more inter
2、mediate shafts(中间轴) and the tailshaft(尾轴).,Main engine,Thrust bearing,Intermediate shaft,Intermediate bearing,Sterntube,Tailshaft,1rudder 2propeller,These shafts are supported by the thrust block(推力轴承), intermediate bearings(中间轴承) and the sterntube bearing (尾轴管轴承).,A sealing arrangement is provided
3、at either end of the tailshaft，with the propeller and cone(锥形物、锥帽) completing the arrangement.,Thrust Block,The thrust block transfers the thrust from the propeller to the hull(船体、壳) of the ship.,It may be an independent unit or an integral(整体的) part of the main propulsion engine.,Both ahead and ast
4、ern thrusts must be catered for(满足(需要).,The casing of the independent thrust block is in two halves which are joined by fitted bolts(紧配螺栓).,Bearing pad,Bearing collar,The thrust loading is carried by bearing pads(推力块).,In some designs the pads extend three quarters of the distance around the collar(
5、 推力环).,The pads are mounted in holders or carriers(架、座、承载装置) and faced with white metal(白合金，巴氏合金).,Other designs employ a complete ring of pads.,Shaft Bearings,Shaft bearings are of two types, the aftermost(靠船尾的) tunnel (轴隧) bearing and all others.,The aftermost tunnel bearing has a top and bottom b
6、earing shell (轴瓦)because,because it must counteract(抵消、克服) the propeller mass and take a vertical upward thrust at the forward end of the shaft.,The other shaft bearings, the intermediate bearings, only support the shaft weight and thus have only lower half bearing shells.,Sterntube Bearing,The ster
7、ntube bearing serves two important purposes.,It supports the tailshaft and a considerable proportion of the propeller weight.,It also acts as a gland(机械密封管) to prevent the entry of sea water to the machinery space.,Early arrangements used bearing materials such as lignum vitae(铁梨木) which were lubric
8、ated by sea water.,Most modern designs use an oil lubrication arrangement for a white metal lined sterntube bearing.,Special seals are fitted at the outboard(舷外的) and inboard(舷内的) ends of the tailshaft.,Oil pressure in the lubrication system is higher than the static sea water head to ensure that se
9、a water cannot enter the sterntube in the event of seal failure.,Propeller,The propeller consists of a boss(桨毂) with several blades of helicoidal(螺旋面) attached(附着，固定于) to it.,When rotated it screws through the water in much the same way as(以和大致相同的方式) a bolt screws through its nut,and thus converts(转
10、换，转变) the engine torque into a direct thrust to push the ship along.,Both the fixed pitch(定螺距) propeller and the variable pitch(变螺距) propeller are used on ship.,A variable pitch propeller(VPP) or controllable pitch propeller(CPP) is made up of a boss(hub) with separate blades mounted into it.,An int
11、ernal mechanism enables the blades to be moved to change the pitch angle.,The great majority of large CPP have their hydraulic servomotor in the hub to operate the blade palms via push rods or a crankpin-sliding block mechanism.,Push rod,Crankpin-sliding block,The hydraulic servomotor is actuated by
12、 a hydraulic circuit and controlled by control valves.,CPP in large vessels are usually fitted with combinative(结合的, 可组合的, 联合的) controls on the bridge.,These are single-lever controls, the single lever controlling both propeller pitch and engine speed,either through pneumatic circuits operated by ca
13、ms driven by a common shaft, or by electronic means.,In either case closed loop circuits are employed, so that feedback, of propeller position and of engine speed, balances off the control signal.,Additional control stands are often fitted on the bridge wings(驾驶室侧翼平台).,These are commonly slaves(从动装置
14、) to the main central bridge control stand.,It is usual practice to take control of both engine and CPP by separate levers in the MCR(main control room) after starting machinery,switching to bridge control from the MCR before leaving harbor.,It follows that the consoles(控制台) housing power supplies e
15、tc. for the CPP controls are generally fitted in the MCR.,READING MATERIAL,FIRE ALARM AND DETECTION (火灾警报与监测),An fire alarm and detection system is required to be installed in the cargo, accommodation and service spaces of,of certain classes of passenger ships and in the cargo spaces of ships carryi
16、ng explosives.,Such systems are also fitted in the machinery spaces of cargo ships specially designed for unmanned operation and on the vehicle decks of certain roll-on, roll-off ships.,The function of a fire detector is to sound alarm whenever it has found a fire.,Fire detectors operating on various different principles are currently available as following:,1. heat detectors which operate at a predetermined temperature;,
