Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERING 



16. When a main shaft is to be unlocked, pre- 

 cautions must be taken to disengage the jacking 

 gear clutch before releasing the brake. If the 

 brake is released first, the main shaft may 

 begin to rotate and cause injury to the turning 

 gear and to personnel. 



17. In an emergency, where the ship is steam- 

 ing at a highspeed, the main shaft can be stopped 

 and held stationary by the astern turbine until 

 the ship has slowed down to a speed at which 

 the main shaft can be safely locked. 



18. Where there is a limiting maximum safe 

 speed at which a ship can steam with a locked 

 propeller shaft, this speed should be known and 

 should not be exceeded. 



19. Before the turning gear is engaged and 

 started, a check should be made to see that 

 the turning gear is properly lubricated. Some 

 ships have a valve in the oil supply line leading 

 to the turning gear. The operator should see 

 that a lube oil service pump is in operation and 

 that the proper oil pressure is being supplied to 

 the turning gear before the motor is started. 



20. It should be definitely determined that 

 the turning gear has been disengaged before the 

 main engines are turned over. 



21. While working on or inspecting open main 

 reduction gears, the person or persons per- 

 forming the work should not have any article 

 about their person which may accidentally fall 

 into the gear case. 



22. Tools, lights, mirrors, etc. used for 

 working on or inspecting gears, bearings, etc. 

 should be lashed and secured to prevent acci- 

 dental dropping into the gear case. 



STEERING 



As noted at the beginning of this chapter, the 

 direction of movement of a ship is controlled 

 partly by steering devices which receive their 

 power from steering engines and partially by 

 the arrangement, speed, and direction of rota- 

 tion of the ship's propellers. 



The steering device is called a rudder . The 

 rudder is a more or less rectangular metal 

 blade (usually hollow on large ships) which is 

 supported by a rudder stock . The rudder stock 

 enters the ship through a rudder post and a 

 watertight fitting, as shown in figure 5-24. A 

 yoke or quadrant , secured to the head of the 

 rudder stock, transmits the motion imparted by 

 the steering mechanism. 



Basically, a ship's rudder is used to attain 

 and maintain a desired heading. The force 

 necessary to accomplish this is developed by 

 dynamic pressure against the flat surface of the 

 rudder. The magnitude of this force and the 

 direction and degree to which it is applied pro- 

 duces the rudder effect which controls stern 

 movement and thus controls the ship's heading. 



In order to function most effectively, a rudder 

 should be located aft of and quite close to the 

 propeller. Many modern ships have twin rud- 

 ders, each set directly behind a propeller to 

 receive the full thrust of water. This arrange- 

 ment tends to make a ship highly maneuverable. 



Three types of rudders are in general use— 

 the unbalanced rudder, the semibalanced rudder, 

 and the balanced rudder. These three types are 

 illustrated in figure 5-25. Other types of rud- 

 ders are also in naval use. For example, some 

 ships have a triple-blade rudder which provides 

 an increased effective rudder area. 



Ill 



