what are Functions of the main parts of ship Propulsion system ? 

1. Thrust shaft :

   The function of the thrust shaft is transferring the revolution motion to the intermediate shaft and transfers the thrust from it to the thrust block.

2. Thrust bearing:

   

   The function of the thrust bearing is transferring propeller thrust to the thrust block casing which is fitted to ship’s hull and causes the ship to move to the thrust direction (forward. or aft).

   Thrust block working theory :

   Thrust collar is forged integrally with the thrust shaft, Thrust pads are fitted in forward and aft side of the thrust collar and they are able to tilt.
   When the shaft rotates, an oil pressure is built up between the white metal face of the thrust pad and the thrust collar, The thrust will transfer from the collar to the thrust pads through the oil film to the casing which is rigid to ship’s hull causing movement of the ship.

3. Stern tube:

   The function of stern tube is to support the weight of the propeller and screw shaft, also prevents sea water to pass through to the ship.

   There are two types of stern tube:

   
   

   A- water lubricating type:

   
   used in this type lignum-vita wood or impregnated resin compound . Lubrication of stern tube takes place when the bearings absorb water and result a wet slippery surface has low friction ratio with high resistance to wear.
   B- oil lubricating type: used in this type lubricating oil which lubricate stern tube bearings, mostly three stage of seals are used to prevent water to enter the ship and prevent oil to escape out of the ship.

4.  Intermediate shaft :

   The function of the intermediate shaft is transmit the rotation from the thrust shaft to the screw shaft (propeller shaft)and
   transmit the thrust from screw shaft to the thrust shaft.

5.  propeller shaft :

   The function of the propeller shaft is transmit the rotation from intermediate shaft to the propeller and transmit the thrust from the propeller to the intermediate shaft.

6.  The Propeller :

   
   

   

   The function of the propeller is to produce the thrust which transmitted to the propeller shaft , That thrust generated due to turning of propeller blades (which have designed angle shape) in the water , some ships have fixed angle propeller , in this type controlling of the ship’s speed is only by controlling main engine speed, Reversing direction ( ahead or astern) is by reversing of engine motion clockwise or anticlockwise , Other ships have controlled pitch propeller which can move propeller blades around their axis, By that way we can reverse ship direction ahead or astern by reversing propeller blades’ angle , also speed can be effected by changing that angle.

7. Shaft bearings:

   The function of shaft bearings to carry shaft weight and to keep it aligned , these bearings are lubricated by oil which is cooled mostly by sea water coils passing in their sumps. Wear of these bearings above limit could cause harmful vibration and shaft misalignment.