Tail Shaft Survey
A tail-shaft survey examines the propeller shaft, bearings, seals and propeller as an assembly. Understanding the installed arrangement helps prepare relevant evidence, distinguish monitoring from survey and follow defects through to an outcome accepted by class.
Operational Explanation
The propeller shaft is the part of the propulsion shafting to which the propeller is fitted. It may connect to a tube shaft, distinct from the intermediate shafts inside the vessel. The stern tube passes through the stern below the waterline and houses bearings and sealing arrangements: bearings support the shaft and allow it to rotate; seals control lubricant leakage and, depending on the arrangement, seawater ingress. A leaking seal, bearing wear and a shaft defect therefore affect different parts of the same system.
The shafting drawing should identify shaft material and protection, bearing positions, seals and propeller connection. A shaft made from approved corrosion-resistant steel is a different case from a common steel shaft protected by approved liners or coatings. The condition of that protection is something to verify, rather than a property inferred from the material’s name.
| Object to identify | What it clarifies for the survey |
|---|---|
| Propeller and connection | Keyed, keyless or flanged connection; accessible areas and required examinations depend on this connection. |
| Shaft, liners and corrosion protection | Component identity and material, relevant surfaces, protection and history of damage or repairs. |
| Bearings and measurement points | Clearance, wear and shaft drop must be related to the specified measurement point and method. |
| Seals, fluid and circuit | Separation from the environment in closed systems, leakage, contamination and lubrication conditions; different arrangements need different data. |
The survey combines physical examination and service history within the applicable method’s scope. Data may support an eligible method or an approved alternative scheme; they do not by themselves demonstrate the absence of every defect. A wear measurement, fluid analysis and surface examination seek different evidence and are not interchangeable. PRS 111/P, §§1.2 and 2.1–3.1.
Instrumentation depends on the manufacturer: for example, Wärtsilä describes water-lubricated composite bearings and a system measuring shaft drop to indicate bearing wear. This illustrates how evidence can be obtained; it does not make that solution or its limits applicable to every vessel. Wärtsilä, bearings and wear-down measurement.
Regulatory Reference
IACS UR Z21 sets unified class requirements for conventional propeller shafts and tube shafts, to be read as incorporated in the vessel’s classification society Rules. The IACS catalogue consulted identifies Rev.4, October 2015 as current: the UR is not by itself an undifferentiated IMO obligation for every vessel. IACS, current version of UR Z21.
UR Z21 distinguishes closed oil- or fresh-water-lubricated systems from open water-lubricated systems. Also identify the propeller coupling, seals and shaft protection: do not transfer methods or monitoring data from a different arrangement. IACS UR Z21.
For example, Method 3 for closed systems requires relevant records and samples together with checks of bearing wear, accessible parts, propeller and seals, and verification of no reported grinding or welding repairs to the shaft/propeller. Check method eligibility in the Rules: a satisfactory oil analysis meets only part of the conditions. IACS UR Z21, 2.1.3.
Method 3 is not available for keyed propeller connections in closed systems. For keyless or flanged connections, eligibility must be read together with the prerequisites and conditions governing the sequence of methods. Open systems have their own Method 4 and conditions related also to shaft configuration and corrosion protection. Interval tables and all their notes belong to the same check: do not extract one common cycle from a single row. PRS 111/P, §§2.3–2.4, table and notes pp10–11; §3, pp11–13.
PRS 111/P, January 2017, remains listed in the current PRS catalogue and is used here as a class cross-check based on Z21 Rev.4, applicable where PRS Rules refer to it; it does not replace other societies’ Rules. The method, due date, any approved alternative means and extension must be established from the vessel’s documents and class decision. Shaft condition monitoring must not be confused with Continuous Machinery Survey. PRS, current Rules and publications catalogue.
Scope of Application
This page supports consultation and familiarisation with conventional shafting, including propeller shafts and tube shafts within the applicable Rules’ scope. Intermediate shafts are outside Z21’s definition of shaft. Pods, azimuth thrusters and other special systems require their own criteria and approved schemes: do not assign the methods described here to them automatically.
Selection starts with the actual installation: closed-loop oil or fresh-water lubrication, or open water lubrication; propeller connection; material, protection, shaft count and relevant service. Also identify any approved alternative means and the conditions for maintaining them. This page does not instruct the reader to withdraw a shaft or authorise opening a seal.
Procedure / How to Complete It
- Reconstruct the arrangement. Connect the approved drawing, component identification, manuals and previous survey report; distinguish the bearing, seal liner and shaft protection. Identify the areas the method must make available for examination.
- Confirm the scope with class. Consult survey status, due date, previous method and applicable Rules. If a different method, alternative scheme or extension is proposed, check every prerequisite and the necessary acceptance: a request does not change the due date.
- Prepare the system dossier. Gather relevant trends and reports: temperatures and oil consumption for an oil-lubricated arrangement; circuit parameters for closed fresh-water lubrication; clearance/wear measurements, leaks, defects and repairs. Distinguish laboratory analysis from examination or sampling required in the Surveyor’s presence; sample point, date, service condition and identity must be traceable.
- Agree preparation and hold points. The vessel’s work plan, SMS and manuals establish competent personnel, coordination with yard and Surveyor and precautions for rotation, energy, openings to the sea, fluids and handling components. Examinations need agreed access and conditions; this list is not an isolation or dismantling sequence.
- Relate each finding to its question. Which surface was seen? Which clearance was measured? Which area does the NDE report cover and by which approved method? Compare evidence with the relevant criteria, documenting access limits, abnormalities and work performed. A wear measurement does not replace crack detection; visual examination does not automatically cover a hidden surface.
- Follow the outcome through to closure. Distinguish completed work, verification results and survey acceptance. Record outstanding defects, class decisions, any conditions and required tests/follow-up after repair or reassembly. Return to service follows the vessel’s authorisation process and applicable conditions; involve the competent Administration/RO if statutory obligations are affected.
Operational responsibilities are defined in the SMS; familiarisation, assignment of tasks, defect management and records have their own role alongside the class decision on the survey. IMO, ISM Code §§6.3, 7, 9 and 10.1–10.2, as amended.
Practical Example
Teaching scenario: a vessel with closed-loop oil lubrication and a keyless propeller connection prepares a survey using a method that also relies on service records. The latest analyses are satisfactory, but the log shows increased oil replenishment and no recorded follow-up to a seal abnormality. The dossier is incomplete: the laboratory result alone does not explain the leak or establish the seal’s condition.
Personnel reconstruct the event, trend, sampling point and available measurements; they inform the designated responsible persons and present the evidence and gaps to class. Class assesses method eligibility and necessary examinations, while Company, vessel and yard arrange work under the agreed plan. The useful outcome is a resolved defect or a formally managed condition, with tests and acceptance documented, rather than simply submitting a “good” analysis.
What Typically Goes Wrong
The usual problem is treating different evidence as though it answered the same question. Regular records do not reveal a crack, a measurement without its point or reference cannot be compared, and unrecorded work changes the history underpinning method eligibility. Report grinding, welding and modifications as well: some surveys expressly require verification that such repairs have not been reported.
Another error is confusing the docking schedule or machinery CMS with the shaft’s due date. An extension needs its own class-prescribed route, distinct from the ordinary survey; it is not obtained by accumulating monitoring data or leaving a request open.
Common Mistakes Mistake Library
| Mistake | Consequence | How to Avoid It |
|---|---|---|
| Use fluid analysis alone to close the survey | Condition of seals, bearings and required surfaces remains unverified | Present records, examinations and results within the accepted method’s scope. |
| Apply Method 3 to every closed system | A method exclusion or condition is overlooked | Check propeller connection, prerequisites and Rule notes. |
| Compare measurements without their point, reference or conditions | The trend may suggest a different level of wear from the actual condition | Keep measurement method, position and conditions with the report. |
| Confuse CMS, completed work or an extension request with a closed survey | Due date and defects may remain outstanding | Check the documented outcome, class decisions and follow-up. |
What the PSCO Checks
Operational Tips
- Keep a dossier for each shaft: identifiers and measurement points must prevent attributing a result to the other side or another component.
- Read service data, fluid examination and physical findings together; report gaps or changed conditions instead of selecting only favourable evidence.
- Keep NDE reports with area, method and result; “checked” without the examination scope does not show what was verified.
- Bring the due date, proposed method, areas to be made accessible and hold points to the preparation meeting; leave the technical sequence to the applicable documents and competent personnel.
Preparation checklist
- Drawing and identification of shaft, propeller/connection, bearings, seals and protection available.
- Lubrication type, material/protection and applicable scheme confirmed for the actual installation.
- Survey status, previous method, due date and any class decisions checked.
- Relevant records, samples/analyses, measurements and leakage or repair history traceable; gaps declared.
- Personnel, safe conditions, access, examinations and hold points agreed in the work plan.
- Defects, work, results, tests/follow-up and survey outcome documented; return to service managed through the prescribed process.
FAQ
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Certified substantive revision: 12 October 2026 · page fingerprint c32c0ed74639