1. Lesson 15 Transmission System

2. Contents Introduction Thrust Bearing Shaft Bearing Sterntube Bearing
Shafting
Propeller
Words & Expressions

3. Introduction
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.

4. Introduction
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 Fig.12.1.

5. Introduction

6. Thrust Bearing
The thrust block transfers the thrust from the propeller to the hull of the ship.
It must therefore be solidly constructed onto a rigid seating or framework to perform its task. It may be an independent unit or an integral part of the main propulsion engine.
Both ahead and astern thrusts must be catered for and the construction must be strong enough to withstand normal and shock loads.

7. Thrust Bearing

8. Thrust Bearing It can limit crankshaft end play.
Thrust flanges are formed on the main bearing sides, almost touching the thrust surfaces machined on the crankshaft.
Absorb axial forces

9. Thrust Bearing
Ball thrust bearing
Roller thrust bearing

10. Shaft Bearing
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.

11. Shaft Bearing

12. Sterntube Bearing The sterntube bearing serves two important purposes.
It supports the tailshaft and a considerable proportion of the propeller weight.
It also acts as a gland to prevent the entry of seawater into the machinery space.

13. Sterntube Bearing
Early arrangements used bearing materials such as lignum vitae (a very dense form of timber), which were lubricated by seawater.
Most modern designs use an oil lubrication arrangement for a white metal lined sterntube bearing.

14. Sterntube Bearing

15. Shafting
There may be one or more sections of intermediate shafting between the thrust shaft and the tailshaft, depending upon the machinery space location.
All shafting is manufactured from solid forged ingot steel with integral flanged couplings.
The shafting sections are joined by solid forged steel fitted bolts.

16. Shafting

17. Propeller

18. Propeller
The propeller consists of a boss with several blades of helicoidal form attached to it.
When rotated it ‘screws’ or thrusts its way through the water by giving momentum to the column of water passing through it.
The thrust is transmitted along the shafting to the thrust block and finally to the ship’s structure.

19. Propeller
Most propellers in the marine industry are made out of aluminum, stainless steel, etc.
There are all sorts of propellers in use today and each one has its own design, the most common is the elephant ear blade.

20. Propeller
Made of hub and blades & creates the thrust necessary to propel the ship through the water
Terms:
Pitch: axial distance advanced during one complete revolution of screw
Face: the pressure side
Back: the suction side

21. Propeller Constant vs. Variable Pitch Fixed vs. Controllable Pitch
Variable has the twisted look
Adv: more efficient over wide range of speeds
Fixed vs. Controllable Pitch
In controllable, blades can rotate on hub to change pitch (change direction)
Right vs. Left Hand Screw
Viewed from aft of ship
Twin-screw ships have one of each

22. Propeller Cavitation Effects
Formation and subsequent collapse of bubbles as propeller turns
Occurs at critical speed
Effects
Excessive noise
Erosion of blades
Decreased efficiency

23. Propeller
Pitch of Propeller

24. Words & Expressions cone n. 螺旋桨轴帽 rigid a. 刚性的 integral a. 整体的，一体的
withstand vt. 承受
pivot v. 转动，滚动
n. 枢轴，支点
holder n. 轴承座/支架
carrier n. 托架
collar n. 轴环

25. Words & Expressions counteract vt. 承受，抵消 bath n. 油槽 transmit vt. 传动，传输
intermediate a. 中间的
propulsion n. 推进，推进力
gland n. 密封压盖
tapered a. 锥形的
helicoidal a 螺旋面
momentum n. 动量

26. Words & Expressions stern tube bearing 尾轴管轴承
intermediate bearing 中间轴轴承
aftermost tunnel bearing 尾轴管轴承
pad stop 停油板
journal bush 轴颈衬套
thrust shaft 推力轴
oil scraper 刮油器
lignum vitae 铁梨木
propeller boss 螺旋桨毂

27. Assignments What does the shafting system consist of?
What is the main function of the transmission system?
What is provided at the end of the tail shaft?
How many types of shaft bearings are there used on ships? What are they?
What purposes does the sterntube bearing serve?
How does propeller drive ships?