PRINCIPLES OF NAVAL ENGINEERING 



precautions should be taken to lock the main 

 shaft. 



11. Where the rotation of the propellers may 

 result in injury to a diver over the side, or in 

 damage to the equipment, propeller shafts should 

 be locked. 



12. When a ship is being towed, the propellers 

 should be locked, unless it is permissible and 

 advantageous to allow the shafts to trail with the 

 movement of the ship. 



13. When a shaft is allowed to turn or trail, 

 the lubrication system must be in operation. In 

 addition, a careful watch should be kept on the 

 temperature within the low pressure turbine 

 casing to see that windage temperatures cannot 

 be built up to a dangerous degree. This can be 

 controlled either by the speed of the ship or by 

 maintaining vacuum in the main condenser. 



14. The main propeller shaft must be brought 

 to a complete stop before the clutch of the turn- 

 ing gear is engaged. (If the shaft is turning, 

 considerable damage to the turning gear will 

 result.) 



15. When the turning gear is engaged, the 

 brake must be set quickly and securely to pre- 

 vent the shaft turning and damaging the turning 

 gear. 



RUDDER STOCK 



PLATFORM DECK 



SHELL PLATING 



BALANCED 



SEMIBALANCED 



UNBALANCED 



Figure 5-24.— Rudder assembly. 



147.52 

 3.99 Figure 5-25.— Balanced, semibalanced, and 



unbalanced rudders. 



110 



