The vessel has its propulsion machinery located amidships, using a water lubricated stern tube bearing, to carry a tail shaft of a 15 inch (38.1 cm) diameter. During the inspection the wear between the stern tube and the bearing surface was measured as 1/4 inch (.635 cm). Which of the following actions should be carried out as a result of this measurement?
• Tail shaft and stern tube clearances for water-lubricated bearings • Typical maximum allowable wear as a fraction of shaft diameter for lignum vitae or rubber bearings • Difference between repair actions: replace vs. buildup vs. no action
• How does the measured clearance (1/4 inch) compare to the shaft diameter (15 inches) as a fraction? Is that within usual marine practice for water-lubricated bearings? • Which component actually wears in a water-lubricated stern tube: the bronze liner on the shaft or the bearing material (like lignum vitae or rubber)? • Would building up a bronze liner versus replacing bearing material be the usual response to EXCESSIVE clearance?
• Calculate clearance as a percentage of shaft diameter and compare with typical guidance for water-lubricated tail shaft bearings. • Identify which part is designed to be the sacrificial/wear component in this system. • Ask whether a professional surveyor would likely pass this as within limits or require corrective action at next drydocking.
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