Tail shaft

The tail shaft, or propeller shaft, is the aftermost section of the propulsion shafting, carrying the propeller at its outboard end and passing through the stern tube and its bearing. It is the highest-stressed shaft section because it carries the propeller weight, the propeller thrust, and the bending from the overhung load, all in a seawater-exposed zone where corrosion-fatigue cracks start, usually at the keyway forward end or the aft liner edge. Forged steel is standard, often with a bronze liner or continuous coating where it runs in a water-lubricated bearing. Class rules set periodic tail-shaft surveys, with the interval extended for oil-lubricated, sealed, and continuously monitored arrangements.