Q9
Explain how the ingress of sea water is prevented in an oil lubricated stern bearing system. Should the system fail, describe the corrective action possible whilst the vessel is afloat. State why two stern bearing oil header tanks are fitted in some instances?
(16)
Reference Answer
### 1. Prevention of Seawater Ingress in an Oil Lubricated Stern Bearing System The prevention of seawater ingress into an oil-lubricated stern tube bearing is primarily achieved by a sophisticated sealing system, commonly known as a Simplex-type seal assembly, located at the aft end of the stern tube. The system works on the principle of maintaining a positive pressure differential between the stern tube lubricating oil and the external seawater. **Key Components and Principles:** * **Chrome Steel Liner:** A hard, corrosion-resistant chrome steel liner is shrunk-fit or keyed onto the propeller shaft. It provides a perfectly smooth and durable running surface for the sealing rings.
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