19. State about stern bearing made from white metal bearing

a. Structure

1.  Propeller shaft

2.  Stern tube

3.  White metal

4.  White metal liners

5.  Oil groove

*White metal material construction:

-A typical analysis of white metal is 3% copper, 7.5% antimony the remain is tin

-The thickness vary according to classification society:

+Lloyd’s register recommends the thickness of 3.8 mm for shaft 300 diameters, up to 7.4 mm for shaft 900 diameters.

+The bearing clearance can be calculated: D1 = 1.001D + 0.5 (mm)

.Where: D1 - Inside diameter of the bearing, D - Outside diameter of the shaft.

*White metal liner must be fixed to the stern tube otherwise it will be turned together with shaft and be soon damaged

*The white metal bearing must be lubricated by lubricating oil.

a.     Advantages of white metal bearing

-Propeller shaft without brass sleeve can be used

-It can withstand heavy load with vibration and changing direction of the shaft

-Corrosion of the shaft is prevented because seawater does not contact with the shaft

-Wear of the shaft is very small. If it is properly lubricated, longevity of the bearing may last 7- 8 years

-Because there are many good features, so nowadays almost big ships use white- metal bearing.

b.  Disadvantages

-Replacing and making is complex

-Sealing and lubricating system for propeller shaft is complex

-Longevity of bearing depends on operating condition, installation standards and especially the sealing.