Answer
Tailshaft tracking protects the ship against catastrophic fatigue failure or oil-pollution scenarios from sterntube bearings. Modern class regimes allow for extended or open-ended tailshaft withdrawals based on rigorous Condition Monitoring (CM).
Continuous Condition Parameters
Sterntube Bearing Temperature: Monitored continuously via forward and aft bearing embedded PT100 sensors. Sudden temperature spikes indicate a breakdown in hydrodynamic oil film lubrication.
Lube Oil Analysis (Parameters Tested):
Water Content: Checked monthly or quarterly. A level above 1% to 2% signals a failure of the forward or aft chrome-steel seal rings, introducing seawater.
Metal Debris / PPM: Monitoring iron (Fe), copper (Cu), and lead (Pb) content indicates wear of the white-metal bearing lining.
Total Acid Number (TAN): Rising acidity shows oil oxidation, which can accelerate chemical pitting on the shaft journal.
Sterntube Oil Consumption Records: Consistent log tracking of header tank oil levels to detect outbound leakage into the sea or inbound oil contamination.