Propeller & Shaft Services

Propeller and stern tube shaft services

Propeller and shaft services cover the inspection, maintenance and repair of the propeller, tailshaft, stern tube bearings and seals, and associated components such as rope guards, intermediate shafts and controllable pitch hubs. These items transmit the full propulsion power of the ship, sit in a harsh environment and are expensive to reach, so problems tend to surface as oil leaks, rising bearing temperatures, vibration or class survey due dates.

vslSafety coordinates propeller specialists, seal makers’ service engineers, shafting contractors and diving teams to attend the vessel afloat or in dry dock, including preparation and support for the class tailshaft survey.

Regulatory requirements and standards

Class surveys of propeller shafts and tube shafts follow IACS Unified Requirement Z21. For oil-lubricated shafts and closed-loop fresh water lubricated shafts, three survey methods are defined. Method 1 involves drawing the shaft and examining the entire shaft, seals and bearings, with non-destructive crack detection at the forward part of the taper and keyway after removing the propeller. Method 2 requires propeller removal and crack detection of the taper but not full withdrawal of the shaft. Method 3 is carried out without removing the propeller, relying on weardown measurements, visual inspection and seal checks. Methods 2 and 3 are only available when prerequisites are met, including review of service records, oil analysis records and an oil sample examination, and no reported repairs by grinding or welding of the shaft or propeller.

For oil-lubricated shafts, UR Z21 requires lubricating oil analysis at intervals not exceeding six months, with records kept on board. Extensions of up to three months, one year or 2.5 years can be granted after an extension survey, subject to limits on how they are combined. For keyless connections using Method 3, UR Z21 caps consecutive Method 3 surveys and sets a maximum 15-year interval between Method 1 or 2 surveys. Water-lubricated open systems are surveyed under Method 4, generally every five years for certain configurations and every three years for others. The ship’s class society applies its own rules based on these requirements, and propeller repairs affecting blade geometry or involving welding should be agreed with class.

Survey and maintenance intervals

Item	Requirement	Interval	Reference
Oil-lubricated tailshaft	Survey by Method 1, 2 or 3 as eligible	Every 5 years, with extension options	IACS UR Z21
Stern tube oil analysis	Laboratory analysis, records on board	Not exceeding 6 months	IACS UR Z21
Keyless propeller, Method 3	Maximum interval between Method 1 or 2 surveys	15 years	IACS UR Z21
Water-lubricated open systems	Method 4 survey	5 or 3 years depending on configuration	IACS UR Z21
Stern bush clearance and seal efficiency	Ascertained and recorded	At bottom examinations	IACS UR Z3

What the service includes

• Stern tube bearing weardown measurement with poker gauge or electronic sensors
• Stern tube oil sampling, laboratory analysis and trend review ahead of the shaft survey
• Inspection and renewal of aft and forward stern tube seals, including afloat seal replacement using habitat or ring systems where available
• Propeller inspection for cavitation, erosion, cracks and bent tips, with repair and static balancing
• Propeller polishing afloat or in dry dock
• Propeller removal and refitting, including hydraulic nut work and push-up records for keyless propellers
• Non-destructive testing of shaft taper, keyway and flange radius during class surveys
• Shaft alignment checks, intermediate bearing inspection and coupling bolt examination
• Controllable pitch propeller hub seal checks and blade bolt inspection

Equipment types covered

Work covers fixed pitch propellers in nickel-aluminium bronze and manganese bronze, controllable pitch propellers, keyed and keyless shaft connections, oil-lubricated white-metal stern tube bearings, water-lubricated composite bearings, and lip-type and face-type seals. Stern tube seal makers commonly encountered include SKF Blohm + Voss, Wärtsilä, Kemel and Eagle Industry. Afloat work is often combined with underwater and diving services, while shaft NDT can be arranged through non-destructive testing (NDT). For engine-side shafting and gearbox work, see engine and machinery overhaul.

Common defects and findings

• Stern tube oil leakage to sea from worn or damaged aft seals, often caused by fishing line or rope
• Water ingress into stern tube oil, detected by rising water content in oil analysis
• Excessive bearing weardown or high aft bearing temperature
• Propeller blade cavitation erosion, cracks at blade roots and bent tips from contact
• Missing or incomplete oil analysis records, preventing use of Method 2 or 3

Certificates and documents you receive

Depending on the job, deliverables include weardown measurement records, oil analysis reports, seal service reports with parts fitted, propeller inspection and repair reports with balancing records, NDT reports, propeller push-up and hydraulic nut records, and photographs. For class surveys, these support the surveyor, who records the shaft survey method and the next due date.

How to prepare the vessel

Check the tailshaft survey due date and eligible methods with class well in advance, and review oil analysis history for gaps. For afloat seal work, confirm the seal maker, size and spares on board, and whether the port permits diving and immobilisation. Trim the vessel if needed to bring the stern tube above water or reduce head pressure, as advised by the seal service engineer. For dry-dock work, provide propeller drawings, push-up data and the previous survey report.

Information needed for a quotation

• Vessel name, IMO number, flag and class
• Port, berth or dry dock, ETA, ETD and draft
• Scope: weardown check, seal renewal, propeller repair or polishing, tailshaft survey support
• Shaft diameter, bearing type, stern tube seal maker, model and size
• Propeller type, diameter, number of blades and material
• Last shaft survey date and method, and recent oil analysis results
• Symptoms such as oil leakage rate, temperatures or vibration

vslSafety coordinates a suitable propeller and shafting provider at the vessel’s port and confirms any maker, diving or class involvement in the quotation.

Frequently asked questions

How often must the tailshaft be surveyed?

For oil-lubricated and closed-loop fresh water lubricated shafts, IACS UR Z21 sets a five-year survey interval using Method 1, 2 or 3 depending on eligibility and connection type, with extension options after an extension survey. Water-lubricated open systems follow Method 4 at five or three years depending on configuration. The class society confirms the applicable method and due date.

Can a stern tube seal be replaced without dry docking?

Often yes. Aft seal rings can be renewed afloat by divers using a habitat or the maker’s underwater replacement system, depending on seal design and water conditions. It usually requires the seal maker’s engineer or an authorised contractor, port permission for diving and propulsion immobilisation. Some damage, such as a scored liner, can only be properly repaired in dry dock.

Why is stern tube oil analysis so important?

Regular analysis detects water ingress, bearing wear metals and oil degradation before they cause bearing failure. Under UR Z21, analysis at intervals not exceeding six months is required for oil-lubricated shafts, and a complete record is a prerequisite for using the less intrusive Method 2 or 3 surveys. Missing samples can force a full shaft withdrawal.

What is poker gauge weardown measurement?

It is a measurement of the gap between the shaft and a reference point on the stern frame, taken with a poker gauge through a plug, or electronically where sensors are fitted. Compared with the reading recorded at installation, it shows how much the aft bearing has worn. It is taken at dry docking, during in-water surveys where possible and at shaft surveys.

Can a damaged propeller be repaired afloat?

Minor damage such as bent tips or edge damage can sometimes be cropped and dressed afloat by divers, with care to keep blade balance. Weld repairs, straightening of heavily bent blades and repairs near the root normally need the propeller removed and are subject to class agreement.