Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERING 



OIL OUTLET OIL OUTLET 

 HUB GEAR \ BOLT / KEY SLEEVE 



\ / / / HUB GEAR 



OIL 

 INLET 

 H. P. TURBINE 

 SHAFT 



SETSCREW 



LOCK NUT 



CRUISING 

 GEAR SHAFT 



HOLES FOR JACKING 

 (USE COUPLING BOLT) 



SECTION A-A 



47,33 



Figure 5-22. — Flexible coupling between cruising gear and high pressure turbine. 



and lock a propeller shaft to prevent damage to 

 the machinery. Wien the shaft is stopped, en- 

 gaging the turning gear and then applying the 

 brake is the most expeditious means of locking 

 a propeller shaft while under way. 



By carrying out actual drills, engineroom 

 personnel should be trained to safely lock and 

 unlock the main shaft. Each steaming watch 

 should have sufficient trained personnel avail- 

 able to stop and lock the main shaft. 



CAUTION: During drills the shaft should not 

 be locked more than 5 minutes, if possible. The 

 ahead throttle should NEVER be opened when the 

 turning gear is engaged. The torque produced by 

 the ahead engines is in the same direction as the 

 torque of the locked shaft; to open the ahead 

 throttle would result in damage to the turning 

 gear. 



The maximum safe operating speed of a ship 

 with a locked shaft can be found in the manufac- 

 turer's technical manual. Additional information 

 on the safe maximum speed that your ship can 

 steam with a locked shaft can be found in Nav - 

 Ships Technical Manual , chapter 9410. If the 

 shaft has been locked for 5 minutes or more, the 

 turbine rotors may have become bowed, and 

 special precautions are recommended. Before 

 the shaft is allowed to turn, men should be sta- 



tioned at the turbines to check for unusual 

 noises and vibration. When the turning gear is 

 disengaged, the astern throttle should be slowly 

 closed, the torque produced by the propeller 

 passing through the water will start the shaft 

 rotating. If, when the propeller starts to turn, 

 vibration indicates a bowed rotor, the ship's 

 speed should be reduced to the point where little 

 or no vibration of the turbine is noticeable and 

 this speed should be maintained until the rotor 

 is straightened. If operation at such a slow 

 speed is not practicable, the turbines should be 

 slowed by use of the astern throttle, to the point 

 of least vibration but with the turbines still 

 operating in the ahead direction. When the tur- 

 bines are slowed to the point of little or no 

 vibration, the shaft should be operated at that 

 speed and the ahead throttle should be opened 

 slightly to permit some steam flow through the 

 affected turbine. The heat from the steam will 

 warm the shaft and aid in straightening it. Low- 

 ering the main condenser vacuum will add addi- 

 tional heat to the turbines; this will increase the 

 exhaust pressure and temperature. 



As the vibration decreases, the astern 

 throttle can be closed gradually, allowing the 

 speed of the shaft to increase. The shaft speed 

 should be increased slowly and a check for 



105 



