PRINCIPLES OF NAVAL ENGINEERING 



STERN 

 DIVEPGENTS 



TRANSVERSE 



WAVES 

 (NOT VISIBLE) 



BOW DIVERGENT 



WAVES 



147.45 

 Figure 5-1. — Bow, stern, and transverse waves. 



relationships of the units required for the de- 

 velopment and transmission of propulsive power. 

 The geared-turbine installation is chosen for this 

 example because it is the propulsion plant most 

 commonly used in naval service today. The same 

 basic principles apply to all types of propulsion 

 plants. 



The units directly involved in the development 

 and transmission of propulsive power are the 



prime mover, the shaft, the propelling device, 

 and the thrust bearing. The various bearings 

 used to support the shaft and the reduction gears 

 (in this installation) may be regarded as neces- 

 sary accessories. 



The prime mover provides the mechanical 

 energy required to turn the shaft and drive the 

 propelling device. The steam turbines shown in 

 figure 5-2 constitute the prime mover of this 

 installation; in other installations the prime 

 mover may be a diesel engine, a gas turbine 

 engine, or a turbine-driven generator. 



The propulsio n shaft provides a means of 

 transmitting mechanical energy from the prime 

 mover to the propelling device and transmitting 

 thrust from the propelling device to the thrust 

 bearing. 



The propelling device imparts velocity to a 

 column of water and moves it in the direction 

 opposite to the direction in which it is desired 

 to move the ship. A reactive force (thrust) is 

 thereby developed against the velocity-imparting 

 device; and this thrust, when transmitted to the 

 ship's structure, causes the ship to move through 

 the water. In essence, then, we may think of 

 propelling devices as pumps which are designed 

 to move a column of water in order to build up 

 a reactive force sufficient to move the ship. The 

 screw propeller is the propelling device used 

 on practically all naval ships. 



The thrust bearing absorbs the axial thrust 

 that is developed on the propeller and trans- 

 mitted through the shaft. Since the thrust bearing 

 is firmly fixed inrelationtothe ship's structure, 

 any thrust developed on the propeller must be 

 transmitted to the ship in such a way as to move 

 the ship through the water. 



WATER 

 COLUMN 



STRUT 

 BEARING 



PROPELLER 



DIRECTION OF 



REACTIVE FORCE 



(THRUST) 



47.42A 



Figure 5-2.— Principles of ship propulsion, 

 86 



