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6. shafting and propellers for the ships pptx
- 1. King Abdul-Aziz University Facultyof Maritime Studies Marine Engineering department Introduction to Marine Engineering (MSE 389) Lecture. 6 Shafting and propellers 1
- 2. 2 Shafting and propellers •The transmission system on a ship transmits power from the engine to the propeller. It is made up of shafts, bearings, and Finally the propeller itself. The thrust from the propeller is transferred to the ship through the transmission system. • The different items in the system include the thrust shaft, one or more intermediate shafts and the tail shaft. These shafts are supported by the thrust block, intermediate bearings and the stern tube bearing. A sealing arrangement is provided at either end of the tail shaft with the propeller and cone completing the arrangement. These parts, their location and purpose are shown in Figure
- 3. 1 Thrust shaft. 2Thrust block. 3 Stern tube. 4 intermediate shaft. 5 Propeller shaft ( screw shaft ). 6 Propeller. 7 Shaft bearing. Shafting and propeller system 3
- 4. 4 What happens whenthe engine runs? when the main engine runs its crankshaft turns the thrust shaft (1) which is connected to it by a heavy flange, the torque is transmitted to the propeller shaft (5) and to the propeller boss (6) through the intermediate shaft (4) . The thrust from the propeller is taken up by the thrust bearing which transmits the thrust to the ship’s hull and causes the ship to be propelled in the direction of the thrust. The thrust block(2) is always fitted at the aft end of the main engine crankshaft.
- 5. 5 Functions of themain parts of Propulsion system 1. Thrust shaft The function of the thrust shaft is to transfer the revolution motion to the intermediate shaft and transfers the thrust from it to the thrust block. 2. Thrust bearing The function of the thrust bearing is to transfer the propeller thrust to the thrust block casing which is fitted to ship’s hull and causes the ship to move to the thrust direction (forward or aft).
- 6. 6 Thrust block • Thethrust block transfers the thrust from the propeller to the hull of the ship. It must therefore be solidly constructed and mounted onto a rigid seating or framework to perform its task. • The casing of the independent thrust block is in two halves which are joined by fitted bolts as shown in figure. The thrust loading is carried by bearing pads which are arranged to pivot or tilt. The pads are mounted in holders or carriers and faced with white metal.
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- 9. 9 Structure of thrustblock • The structure under the thrust block is reinforced with steel plates and I-beams above and inside the double bottom tanks or cofferdams. • The thrust block itself consists of a housing which contains a number of wedge-shaped white metal pads with generous helical oil grooves cut into them. • The pads are arranged and fixed around a steel support, holding them against a machined collar on the drive shaft.
- 10. 10 Structure of thrustblock • The pads are prevented from overheating and premature wear by a fluid film of oil between them and the collar, with the oil supply being hydrodynamic (self-pressurized) due to the rotation of the drive shaft. • There is an oil reservoir in the bottom of the housing which may contain an oil-cooling coil through which seawater is circulated.
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- 13. 13 Stern tube 3. Sterntube The function of stern tube is to support the tail shaft and a proportion of the propeller weight. It also acts as a gland to prevent the entry of sea water to the machinery space. A- water lubricating stern tube type used in this type lignum-vita wood which a very dense form of timber which were lubricated by sea water. B- oil lubricating stern tube type Most modern designs use an oil lubrication arrangement for a white metal lined stern tube bearing. Special seals are fitted at the outboard and inboard ends of the tail shaft. They are arranged to prevent the entry of sea water and also the loss of lubricating oil from the stern bearing.
- 14. 14 4. Intermediate shaft Thefunction of the intermediate shaft is to transmit the rotation from the thrust shaft to the propeller shaft and transmit the thrust from the propeller shaft to the thrust shaft. 5. propeller shaft The function of the propeller shaft is to transmit the rotation from intermediate shaft to the propeller and transmit the thrust from the propeller to the intermediate shaft.
- 15. 15 Purpose and Operationof the Propeller Shaft • The propeller shaft is bolted to the main engine flywheel, passing through the thrust block then along the shaft tunnel. Here it is supported by the shaft bearings before passing through the stern tube to drive the ship's propeller. • The shaft complete is manufactured from forged steel, with coupling flanges. It is machined leaving a larger diameter at the location of the shaft bearings; this section has to have a fine finish to run within the white metal bearing.
- 16. 16 Purpose and Operationof the Propeller Shaft • The shaft coupling flange faces are accurately machined and the bolt holes reamed to accept fitted bolts. They are bolted together using high tension bolting, which is tightened using hydraulic tensioning gear. • The supporting bearings are cast in two halves and are usually white metal lined. These have oil scrolls cut into them to distribute the splash lubrication. Nowadays ball bearing shaft supports are being used, but they have been reported as being quite noisy with a tendency to run hot.
- 17. 17 Purpose and Operationof the Propeller Drive Shaft • The propeller shaft has a CUNI (copper nickel alloy) liner shrunk onto it. Babbitt metal is applied over this and then machined, providing the bearing surface between the cast iron stern tube and the propeller shaft. This is lubricated and cooled by lube oil supplied from a gravity tank located under the aft peak. The propeller shaft has mechanical and/or adjustable gland seals fore and aft to prevent the ingress of oil to the sea and the aft bilge well.
- 18. 18 6. The Propeller •The function of the propeller is to produce the thrust which transmitted to the propeller shaft , that thrust generated due to turning of propeller blades (which have designed angle shape) in the water , some ships have fixed angle propeller , in this type controlling of the ship’s speed is only by controlling main engine speed, Reversing direction ( ahead or astern) is by reversing of engine motion clockwise or anticlockwise. • Other ships have controlled pitch propeller which can move propeller blades around their axis, by that way we can reverse ship direction ahead or astern by reversing propeller blade’s angle , also speed can be effected by changing that angle.
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- 20. 20 7. Shaft bearings •The function of shaft bearings to carry shaft weight and to keep it aligned , these bearings are lubricated by oil. Cooling of the bearing is by water circulating through a tube cooler in the bottom of the casing. Wear of these bearings above limit could cause harmful vibration and shaft misalignment. • Shaft bearings are of two types, the aftermost tunnel bearing and all others. • The aftermost tunnel bearing has a top and bottom bearing shell because it must counteract the propeller mass and take a vertical upward thrust at the forward end of the tail shaft. • The other shaft bearings only support the shaft weight and thus have only lower half bearing shells.
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- 25. 25 Purpose and Operationof Stern Tube • The stern tube is used to support and seal the propeller shaft as it passes through the aft hull. • It consists of a cast iron tube welded into the stern frame. In the old days, the shaft inside the tube was bronze coated and run against a longitudinal bearing, which, was made of narrow strips of a very hard wearing wood known as “lignum vitae.”
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- 27. 27 Assignment # 6 1.What are the main functions of ship power transmission system? 2. What are the main functions of the following ship propulsion components: i. Thrust block ii. Thrust shaft iii. Thrust bearing iv. Stern tube v. Intermediate shaft vi. propeller shaft vii. Propeller viii. Shaft bearings 3. Explain with drawing the operations of the following ship power transmission systems: a) Thrust block b) Stern tube
- 28. 4. Write thename of the main components of ship propulsion system from 1 to 7? 28