Principles of naval engineering - Historic Naval Ships Association

Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERING16. When a main shaft is to be unlocked, precautionsmust be taken to disengage the jackinggear clutch before releasing the brake. If thebrake is released first, the main shaft maybegin to rotate and cause injury to the turninggear and to personnel.17. In an emergency, where the ship is steamingat a highspeed, the main shaft can be stoppedand held stationary by the astern turbine untilthe ship has slowed down to a speed at whichthe main shaft can be safely locked.18. Where there is a limiting maximum safespeed at which a ship can steam with a lockedpropeller shaft, this speed should be known andshould not be exceeded.19. Before the turning gear is engaged andstarted, a check should be made to see thatthe turning gear is properly lubricated. Someships have a valve in the oil supply line leadingto the turning gear. The operator should seethat a lube oil service pump is in operation andthat the proper oil pressure is being supplied tothe turning gear before the motor is started.20. It should be definitely determined thatthe turning gear has been disengaged before themain engines are turned over.21. While working on or inspecting open mainreduction gears, the person or persons performingthe work should not have any articleabout their person which may accidentally fallinto the gear case.22. Tools, lights, mirrors, etc. used forworking on or inspecting gears, bearings, etc.should be lashed and secured to prevent accidentaldropping into the gear case.STEERINGAs noted at the beginning of this chapter, thedirection of movement of a ship is controlledpartly by steering devices which receive theirpower from steering engines and partially bythe arrangement, speed, and direction of rotationof the ship's propellers.The steering device is called a rudder . Therudder is a more or less rectangular metalblade (usually hollow on large ships) which issupported by a rudder stock . The rudder stockenters the ship through a rudder post and awatertight fitting, as shown in figure 5-24. Ayoke or quadrant , secured to the head of therudder stock, transmits the motion imparted bythe steering mechanism.Basically, a ship's rudder is used to attainand maintain a desired heading. The forcenecessary to accomplish this is developed bydynamic pressure against the flat surface of therudder. The magnitude of this force and thedirection and degree to which it is applied producesthe rudder effect which controls sternmovement and thus controls the ship's heading.In order to function most effectively, a ruddershould be located aft of and quite close to thepropeller. Many modern ships have twin rudders,each set directly behind a propeller toreceive the full thrust of water. This arrangementtends 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 areillustrated in figure 5-25. Other types of ruddersare also in naval use. For example, someships have a triple-blade rudder which providesan increased effective rudder area.Ill