Tài liệu Lesson 13-The Propulsion Plant pdf

Lesson 13-The Propulsion Plant

The ship propulsion plant denotes the whole plant that transfers to the propeller the

power turned out by main engines.

Marine diesel engines are generally of high rpm, rpm being the short form for

revolution per minute. As far as rpm is concerned, it might be out of your expectation that

if M. E. rpm is too high, the efficiency of a propeller will be reduced on the opposite, for

the propeller rpm of an ocean-going vessel will normally range from 100 to 200.

Therefore, the propulsion plant concerns not only a matter of drive but a problem of the

speed reduction and clutch.

The propulsion plant in practical service nowadays mainly includes the following

types:

1. Direct Drive

With simple and reliable construction, convenient operation, less energy loss during

drive and high propulsion efficiency, direct drive is the most common drive type and has

found a wide application.

In respect of direct drive, the shaft system is directly connected with M. E. thrust

shaft and both of them obtain the same rotating direction. Comparatively speaking, direct

drive is suitable for a lowspeed diesel engine.

2. Gear Drive

The merits of gear drive are as clear as daylight, for M: E. rpm will be free from the

low rpm limitation of a propeller after speed reduction by means of a gear and better

Fig. 13.1

1-flywheel;2-intermediate shaft; 3-stern shaft; 4-propeller

propulsion efficiency can thus be maintained. The only trouble with gear drive is that the

size and weight of a reduction gearbox will inevitably and correspondingly be increased

accompanying the steady increase of M. E. power. As a result of this, its manufacture

process will run into difficulty, since the maximum diameter of a gear for a 35-50 kW

reduction unit may be as large as over 5 meters.