Tail Shaft Survey
The five-year cycle of the tail shaft hides an important technical choice: traditional survey with withdrawal, or Continuous Machinery Survey to spread the inspection over time?
Operational Explanation
The tail shaft transmits power from the engine to the propeller, passing through the stern tube that separates it from seawater. The periodic survey verifies the integrity of the shaft, seals, and support bushes, with a standard 5-year cycle, typically coinciding with the Special Survey in dry dock.
For oil-lubricated shafts, some checks can generally be carried out afloat; for grease- or water-lubricated shafts, some measurements require withdrawal in dock. The choice between the traditional survey cycle and the Continuous Machinery Survey (CMS), which spreads inspections over time according to a programme agreed with Class, depends on the ship's technical configuration and the Company's maintenance strategy.
Regulatory Reference
Requirements of the applicable Classification Society (implementing the IACS UR Z series) for tail shaft survey: standard five-year cycle, with the option of Continuous Machinery Survey (CMS) as an alternative to spread inspections.
Scope of Application
Every ship fitted with a tail shaft with stern tube, according to the survey cycle applicable to the specific technical configuration (type of lubrication, presence of continuous monitoring systems).
Procedure / How to Complete It
- Verify the shaft's technical configuration (type of lubrication, presence of monitoring sensors) to determine the applicable survey cycle.
- Plan shaft withdrawal (if required by the traditional cycle) to coincide with the scheduled dry dock entry.
- Measure bush clearances against the permissible limits of the Classification Society.
- Inspect stern tube seals for signs of wear or leakage, replacing them if necessary.
- For ships under CMS regime, verify that the continuous monitoring programme (oil analysis, temperature/vibration sensors) has been followed according to agreed intervals.
Practical Example
Example of survey: an oil-lubricated tail shaft, verified under CMS regime with quarterly oil analysis and continuous temperature monitoring, without needing full withdrawal, barring contrary indications from the monitoring data.
Real Cases
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Shaft survey cycle not coordinated with the scheduled dry dock entry | Need for an additional dock dedicated solely to the tail shaft survey | Always coordinate the shaft's cycle with overall dry dock planning |
| Continuous monitoring data (CMS regime) collected but not systematically analyzed | Deterioration trend not detected in time | Systematically analyze monitoring data according to intervals agreed with Class |
| Stern tube seals not thoroughly inspected to save dock time | Risk of lubricant leakage or seawater ingress before the next survey | Never reduce seal inspection for time reasons |
PSC Observations
Operational Tips
- Always coordinate the tail shaft survey cycle with overall dry dock planning.
- If under CMS regime, systematically analyze monitoring data, don't just collect it.
- Never compress stern tube seal inspection to save dock time.
Checklist
- Shaft's technical configuration verified to determine the applicable survey cycle
- Shaft withdrawal (if required) coordinated with dry dock entry
- Bush clearances measured against permissible limits
- Stern tube seals inspected and replaced if necessary
- CMS programme (if applicable) followed and data systematically analyzed