Shaft Alley

The shaft alley, sometimes called the shaft tunnel, is a watertight enclosed passageway that runs longitudinally through the after cargo holds or ballast tanks, enclosing the propeller shaft between the engine room aft bulkhead and the stern tube forward bearing. It must be watertight and fitted with an access manhole or escape so that watchkeepers can inspect intermediate shaft bearings and the sterntube aft seal at sea. SOLAS Chapter II-1 requires that the shaft tunnel maintain the subdivision integrity of the ship by being treated as a floodable space in stability calculations. Engineers walk the shaft alley regularly to check bearing temperatures, listen for unusual noise or vibration, and verify that the bilge in the tunnel does not contain excessive oily water. Intermediate shaft bearings in the tunnel are lubricated by oil rings or grease nipples and must be topped up on schedule. The shaft alley also routes pipework and sometimes electrical cables, so fire detection and ventilation to prevent accumulation of flammable vapour are required by SOLAS II-2.