Lesson 15 Transmission System

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

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.

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.

Introduction

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.

Thrust Bearing

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

Thrust Bearing Ball thrust bearing Roller thrust bearing

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.

Shaft Bearing

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.

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.

Sterntube Bearing

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.

Shafting

Propeller

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.

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.

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

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

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

Propeller Pitch of Propeller

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

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

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

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?