Principles of naval engineering - Historic Naval Ships Association

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGOIL OUTLET OIL OUTLETHUB GEAR \ BOLT / KEY SLEEVE\ / / / HUB GEAROILINLETH. P. TURBINESHAFTSETSCREWLOCK NUTCRUISINGGEAR SHAFTHOLES FOR JACKING(USE COUPLING BOLT)SECTION A-AFigure 5-22. — Flexible coupling between cruising gear and high pressure turbine.47,33and lock a propeller shaft to prevent damage tothe machinery. Wien the shaft is stopped, engagingthe turning gear and then applying thebrake is the most expeditious means of lockinga propeller shaft while under way.By carrying out actual drills, engineroompersonnel should be trained to safely lock andunlock the main shaft. Each steaming watchshould have sufficient trained personnel availableto stop and lock the main shaft.CAUTION: During drills the shaft should notbe locked more than 5 minutes, if possible. Theahead throttle should NEVER be opened when theturning gear is engaged. The torque produced bythe ahead engines is in the same direction as thetorque of the locked shaft; to open the aheadthrottle would result in damage to the turninggear.The maximum safe operating speed of a shipwith a locked shaft can be found in the manufacturer'stechnical manual. Additional informationon the safe maximum speed that your ship cansteam with a locked shaft can be found in Nav -Ships Technical Manual , chapter 9410. If theshaft has been locked for 5 minutes or more, theturbine rotors may have become bowed, andspecial precautions are recommended. Beforethe shaft is allowed to turn, men should be stationedat the turbines to check for unusualnoises and vibration. When the turning gear isdisengaged, the astern throttle should be slowlyclosed, the torque produced by the propellerpassing through the water will start the shaftrotating. If, when the propeller starts to turn,vibration indicates a bowed rotor, the ship'sspeed should be reduced to the point where littleor no vibration of the turbine is noticeable andthis speed should be maintained until the rotoris straightened. If operation at such a slowspeed is not practicable, the turbines should beslowed by use of the astern throttle, to the pointof least vibration but with the turbines stilloperating in the ahead direction. When the turbinesare slowed to the point of little or novibration, the shaft should be operated at thatspeed and the ahead throttle should be openedslightly to permit some steam flow through theaffected turbine. The heat from the steam willwarm the shaft and aid in straightening it. Loweringthe main condenser vacuum will add additionalheat to the turbines; this will increase theexhaust pressure and temperature.As the vibration decreases, the asternthrottle can be closed gradually, allowing thespeed of the shaft to increase. The shaft speedshould be increased slowly and a check for105