Operational Guide · Registers & Logbooks

# 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?

tail shaft tail shaft stern tube CMS

## 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

1. Verify the shaft's technical configuration (type of lubrication, presence of monitoring sensors) to determine the applicable survey cycle.
2. Plan shaft withdrawal (if required by the traditional cycle) to coincide with the scheduled dry dock entry.
3. Measure bush clearances against the permissible limits of the Classification Society.
4. Inspect stern tube seals for signs of wear or leakage, replacing them if necessary.
5. 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

Severe tail shaft or stern tube seal damage, resulting in seawater ingress into the stern tube or lubricating oil leakage into the sea, has in several cases been traced to a survey postponed beyond the planned cycle, or to a CMS regime with monitoring data not adequately analyzed over time.

## 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

The tail shaft survey is not typically subject to direct PSC verification, but its validity is part of the overall Class certification verifiable at every inspection.

## 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

## FAQ

What is the standard tail shaft survey cycle?
Typically 5 years, often coinciding with the Special/Renewal Survey in dock, unless the Continuous Machinery Survey (CMS) regime is adopted, which spreads inspections over time.
What is Continuous Machinery Survey (CMS) for the tail shaft?
An alternative to the traditional five-year cycle, involving continuous monitoring (oil analysis, sensors) according to a programme agreed with the Classification Society, reducing the need for full withdrawals at fixed intervals.
Do grease- or water-lubricated shafts always require withdrawal in dock?
Typically yes, unlike some oil-lubricated shafts which can benefit from partial checks afloat or CMS regimes, according to the specific criteria of the applicable Classification Society.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Bottom Survey and In-Water Survey Rudder and Sea Chests

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