Lesson 25• Shafting( 轴系 ) And Propelle

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• 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 intermediate shafts(中间轴 ) and the tailshaft(尾轴 ).

Main engine

Thrust bearing

Intermediate shaft

Intermediate bearing

Sterntube

Tailshaft

1—rudder2—propeller

• 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 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 fro

m 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 astern 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 padBearing pad

Bearing collarBearing 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( 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 after

most(靠船尾的 ) tunnel (轴隧 ) bearing and all others.

• The aftermost tunnel bearing has a top and bottom bearing 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 sterntube bearing serves two import

ant 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 lubricated 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 sea 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 internal 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 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 cams 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 )' 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 etc. 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 carrying 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;

• 2. heat detectors which operate when the rate of temperature rise of the surrounding air reaches a set limit;

• 3. smoke detectors which operate when smoke obscures(使暗 ; 遮掩 ) a beam of light falling on a photoelectric cell( 光电管 );

• 4. smoke detectors which operate when a beam of light is scattered( 散射 ( 光、热等 )) by smoke and caused to fall on a photoelectric cell;

• 5. combustion products detectors which operate when an electric through an ionized(使离子化 ) atmosphere is changing;

• 6. flame detectors which react to radiation(放射物 ; 辐射线 [能 ]) emanating(散发 , 放射 ) from flame.

• B. FIRE EXTINGUISHING APPLIANCES

Water Pumps, Water Pumps, Hydrants(Hydrants( 消 防消 防栓栓 )) and Hoses and Hoses

• Most ships have an arrangement of fire main and hydrant valves whereby at least two jets of water may be directed on a fire in any part of the ship.

• The water supply to the fire main is generally provided by at least two power operated pumps in the machinery spaces,

• together with an alternative supply which can be brought into operation should the engine room be untenable(不能维持的 ).

• This is usually provided by a separate auxiliary pump (emergency pump) driven by a diesel engine or by an electric motor coupled to an emergency generator.

• The deck main has a drain at the lowest position so that the pipe can be emptied in cold weather.

• If this is not done, the pipe can be damaged by the water freezing, but more important, it will be blocked by the ice and not usable.

• Fire hoses must be of approved material. They are positioned adjacent to hydrants together with suitable nozzles.

• Dual purpose nozzles can be adjusted by rotation of the sleeve ( 外套壳 )to produc

e a jet or spray.

• These are an alternative to having one nozzle for a jet and another for a spray or fog to be used for oil fires.

Portable Portable Extinguishers(Extinguishers( 熄灭者熄灭者 , , 灭火器灭火器 ))

• There are many types of portable extinguisher used on board ship.

• Soda-acid extinguishers are useful on carbonaceous(碳的 , 碳质的 ) fires, usually in accommodation, involving wood, paper and furnishings,

• where the primary purpose is to reduce the temperature of the burning material by projecting a jet of water on it.

• With oil fires however, such a jet of water is not effective as it disturbs the surface and spreads the oil.

• The chemical foam extinguisher can be used to deal with the oil fires.

• It is usually found in machinery spaces and other locations where an oil fire may occur.

• Carbon dioxide extinguishers and dry powder extinguishers are very useful on chemical fires.

• Halogenated hydrocarbon extinguishers(卤化烃类灭火器 ) may be found in such positions as radio rooms and switch boards.

Fixed Installations Fixed Installations • The accommodation and service spaces a

re required being fitted with an automatic sprinkler(洒水装置 ) and fire alarm system.

• The water spray systems are used for machinery spaces and vehicle decks.

• The foam smothering(窒息 ) system may be used for the boiler room or engine room.

• Carbon dioxide smothering systems are used for cargo or machinery spaces.

• Besides, dry powder systems and funnel inerting(惰性的 ) systems can also be found.