Exam Question

The stern tube lubrication system is a critical arrangement designed to lubricate the propeller shaft bearings within the stern tube, prevent ingress of seawater into the vessel, and prevent leakage of lubricating oil into the marine environment. It ensures the smooth and efficient rotation of the propeller shaft while supporting the shaft's weight and resisting propeller thrust.
### 1. Concept and Principles
The stern tube houses the propeller shaft, which connects the main engine (or gearbox) to the propeller. The shaft runs through the stern tube, supported by bearings. These bearings require continuous lubrication to minimize friction, dissipate heat, and prevent wear. The lubrication system typically utilizes a positive pressure head, maintained by a header tank, to ensure a constant supply of oil to the bearings and to create an oil barrier against seawater.
### 2. Main Components and Their Functions