Stern Tube and Stern Tube Bearings

Chapter  4—REDUCTION  GEARS  AND  RELATED  EQUIPMENT grooved to accommodate the rings. As they glide through  the  reservoir  of  oil  at  the  bottom,  the rings carry some of the oil along to the top of the shaft  journal. On some steam driven ships, the most recent line  shaft  bearing  design  employs  oiler  discs instead of oiler rings for lubrication. At very low speeds (i.e., when the shaft is jacked for 24 hours while the turbines are cooling), the oil rings tend to slip and lubrication is sometimes inadequate. The oiler discs are clamped to propulsion shaft and have cavities at the periphery which carry oil to the top of the bearing regardless of the shaft speed. Spring  bearing  temperatures  and  oil  levels should be checked hourly while underway. At least  once  each  year,  the  bearings  should  be inspected,  clearances  taken,  and  any  defects corrected. STERN TUBE AND STERN TUBE  BEARINGS The  hole  in  the  hull  structure  for  accom- modating the propeller shaft to the outside of the hull is called the stern tube. The propeller shaft is  supported  in  the  stern  tube  by  two  bearings— one at the inner end and one at the outer end of the stern tube—called stern tube bearings. At the inner end of the stern tube there is a stuffing box containing  the  packing  gland  (figure  4-4),  which is generally referred to as the stern tube gland. The stern tube gland seals the area between the shaft and stern tube but allows the shaft to rotate. The stuffing box is flanged and bolted to the stern   tube.   Its   casing   is   divided   into   two compartments—the forward space which is the stuffing box proper, and the after space, provided with  a  flushing  connection,  designed  to  maintain a positive flow of water through the stern tube for   lubricating,   cooling,   and   flushing.   This flushing  connection  is  supplied  by  the  firemain. A DRAIN CONNECTION is provided both for testing for the presence of cooling water in the bearing  and  for  permitting  sea  water  to  flow through the stern tube and cool the bearing when underway, where natural seawater circulation is employed. The  gland  for  the  stuffing  box  is  divided longitudinally into two parts. The gland bolts are long enough to support the gland when the latter is withdrawn at least 1 inch clear of the stuffing Figure  4-4.—Stern  tube  stuffing  box  and  gland. 4-9


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