Stern Tube Seal
critical
IMO Required
12 models total
A stern tube seal is the last barrier between the sea and the ship's interior where the propeller shaft passes through the hull, and unlike a bearing it is a wear item by design — the sealing lips or faces are meant to wear against a liner that must itself be renewed on a schedule.
Read more — Stern Tube Seal explained ▾
What the stern tube seal actually does
The stern tube seal keeps seawater out of the stern tube and, on oil-lubricated systems, keeps lubricating oil from leaking into the sea. It sits where the rotating propeller shaft passes through the stationary stern tube, so it must seal a moving surface continuously, at whatever depth the propeller sits below the waterline, for years between dry dockings. Two designs dominate: lip-type seals, where several spring-loaded rubber lips ride against a shaft liner, and face-type (mechanical) seals, where a rotating and a stationary carbon or bronze face are held together by springs and hydraulic pressure. Face seals tolerate more shaft misalignment and are now standard on larger tonnage; lip seals remain common on smaller vessels for their lower cost.
Main components
Seal rings or lip elements
A lip-type unit typically has an aft set of lips facing the sea and a forward set facing the stern tube lubricant, with a drain between them to catch and monitor any leakage past the outboard lips before it becomes a pollution event.
Shaft liner or sleeve
The sealing surface itself, a bronze or stainless steel liner shrunk or bonded onto the shaft, must be smooth and free of pitting; the seal element wears against this liner, not against the shaft steel.
Housing and spring-loaded faces (face seals)
In a face-type seal the housing carries the stationary ring while a rotating ring turns with the shaft, held in contact by springs; a header tank supplies sealing oil at a small positive pressure above sea pressure so any leakage path runs oil outward, not seawater inward.
Selection and sizing
The seal is matched to the shaft, not chosen independently:
- Shaft diameter and the operating depth of the propeller, which sets the sea pressure the aft seal faces must hold.
- Lubrication type of the stern tube, oil or water, since seal materials and drain arrangements differ between the two.
- Maximum allowable shaft misalignment and whirl, particularly on ships with a long, flexible shaft line.
- Air seal option for dry-docking, allowing compressed air to be admitted between seal sets so the vessel can be surveyed afloat rather than always in dry dock.
Regulations and class
MARPOL Annex I addresses oil-lubricated stern tubes as a pollution source, which is one reason the industry has shifted toward water-lubricated systems or seal designs with a monitored oil-to-sea interface. Class rules require periodic survey of the stern tube seal and shaft, typically tied to a five-year special survey cycle, with a tailshaft survey interval that can be extended if continuous shaft condition monitoring is fitted and approved. Oil content in any overboard drain from the seal system is subject to the same discharge limits as other machinery space bilge water.
Typical faults
| Fault | Consequence |
|---|---|
| Worn or hardened lip elements | Increasing seawater ingress into the stern tube, diluting or contaminating the lubricant |
| Scored or pitted shaft liner | New seal lips wear rapidly against the damaged surface and leakage returns within months |
| Loss of sealing oil header pressure | Pressure balance reverses, allowing seawater to enter past the aft face seal |
| Shaft misalignment beyond seal tolerance | Uneven wear on the sealing faces and premature failure on one side only |
| Blocked drain between lip sets | Leakage is not detected early because the monitoring point itself is fouled |
What to look for in a supplier
- Exact liner and seal dimensions matched to the shaft as fitted, since aftermarket seals built to a slightly different tolerance shorten life significantly.
- Experience with underwater seal replacement by divers where dry-docking is not scheduled, if the vessel needs the work done afloat.
- Availability of the correct sealing oil grade and a supply plan for the header tank, not just the seal hardware itself.
- A record of class approval for the specific seal type, since an unapproved substitute can complicate the tailshaft survey.
Track the trend in stern tube oil consumption and water content over months, not just the pass or fail at survey; a slowly rising water percentage in the lubricant is the seal telling you it is wearing out long before it leaks visibly.
8000h
Service Interval
5 yr
Class Survey
10 yr
Typical Lifetime
Typical Manufacturers
Wartsila
Blohm+Voss
Kemel
Duramax
5 manufacturers · 12 models
SKF
8
SKF Simplex Compact C200
unverified
· compact stern tube seal
Seal type
compact stern tube seal
Shaft diameter
200 mm
Application
marine stern tube sealing
Strengths
- Compact design saves space within the stern tube assembly
- Integrated bearing support simplifies installation and alignment
- Low friction reduces power loss and improves fuel efficiency
- Replaceable sealing elements enable straightforward maintenance
- SKF’s proven material quality offers long service intervals
Weaknesses
- Limited to shaft diameters up to about 250 mm, unsuitable for larger shafts
- Single‑lip configuration provides lower pressure capability than some double‑lip designs
- Requires precise alignment during installation to avoid premature wear
- May need a dedicated lubrication system for optimal performance
- Higher initial purchase price compared with basic rubber lip seals
Typical Vessels:
Product TankerContainer ShipBulk CarrierOffshore Supply VesselGeneral Cargo Ship
Decision Guide: Choose if: you need a space‑saving seal for shafts up to 200 mm, value low friction and easy maintenance, and operate on vessels where power efficiency is critical. Avoid if: the shaft diameter exceeds the seal’s rating, high pressure or extreme temperature conditions are expected, or budget constraints favor simpler rubber seals.
Use Cases: Commonly installed in new‑builds and retrofits where stern tube space is limited, such as medium‑speed product tankers and container vessels. It is favored for routes requiring fuel efficiency and for ships that undergo regular maintenance cycles, allowing quick seal element replacement without major disassembly.
SKF Simplex Compact C300
unverified
· compact stern tube seal
Seal type
compact stern tube seal
Shaft diameter
300 mm
Application
marine stern tube sealing
Strengths
- Very small axial length – ideal where space inside the stern tube is restricted
- Dual‑lip, spring‑loaded design gives reliable sealing over a wide pressure range
- Low friction and reduced wear extend service intervals and lower maintenance costs
- Easy retrofit onto existing SKF bearing arrangements; compatible with standard lubrication systems
- Robust against moderate shaft misalignment and vibration
Weaknesses
- Higher unit cost compared with basic single‑lip seals
- Installation requires careful alignment and torque control to achieve full performance
- Limited to shaft diameters up to about 400 mm; not suitable for larger shafts
- May need a dedicated seal oil supply or pressure regulator in some applications
- Not intended for extremely high‑speed shafts (>200 rpm) where heat buildup can be critical
Typical Vessels:
TankerBulk CarrierContainer ShipGeneral Cargo VesselOffshore Supply VesselCruise Ship
Decision Guide: Choose if: you need a reliable seal for a 300 mm shaft in a confined stern‑tube space, value low maintenance and long intervals, and already use SKF bearings. Avoid if: the shaft size exceeds the design limit, budget constraints demand the cheapest seal option, or the vessel operates at very high shaft speeds requiring specialised high‑temperature seals.
Use Cases: The C300 is typically installed during new‑build construction of merchant vessels where the stern tube geometry is tight, and it is also a common choice for retrofits during dry‑docking when upgrading to a more compact, low‑leakage solution without major hull modifications.
SKF Simplex Compact C400
unverified
· compact stern tube seal
Seal type
compact stern tube seal
Shaft diameter
400 mm
Application
marine stern tube sealing
Strengths
- Compact design saves installation space in the stern tube area
- Integrated bearing reduces component count and simplifies maintenance
- Low friction operation improves propeller efficiency
- Optimised for shaft diameters up to 400 mm with high sealing reliability
- Oil‑lubricated system provides easy routine servicing
Weaknesses
- Rated primarily for medium‑speed vessels; not ideal for high‑speed applications
- Maximum pressure rating lower than heavy‑duty, high‑thrust seals
- Requires precise alignment and correct oil supply during installation
- Higher initial purchase cost compared with basic lip seals
- Not suitable for shafts larger than 500 mm
Typical Vessels:
Bulk CarrierProduct TankerContainer ShipGeneral Cargo VesselOffshore Supply VesselFerry
Decision Guide: Choose the Simplex Compact C400 when you need a space‑saving, low‑maintenance seal for a 400 mm shaft on medium‑speed vessels and can provide proper oil lubrication. Avoid it for high‑speed ships, very high thrust loads, or when shaft diameters exceed its rating.
Use Cases: Commonly installed in the stern tubes of tankers, bulk carriers and container ships to prevent seawater ingress while allowing smooth rotation of the propulsion shaft; also used on offshore support vessels where compactness and ease of maintenance are critical.
SKF Simplex Compact C500
unverified
· compact oil‑lubricated mechanical seal
Seal type
compact stern tube seal
Shaft diameter
500 mm
Application
marine stern tube sealing
Strengths
- Very small axial length – allows reduced stern‑tube diameter and saves space
- Low friction carbon/metal sealing faces give high efficiency and low power loss
- Oil‑lubricated design provides excellent wear resistance and long service intervals
- Rated for pressures up to ~30 bar, suitable for most medium‑speed marine applications
- Straight‑forward installation with SKF’s standard mounting kit
Weaknesses
- Requires a reliable oil supply system; not suited for water‑lubricated installations
- Maximum shaft speed limited (typically ≤200 rpm) – unsuitable for high‑speed shafts
- Higher upfront cost compared with simple lip seals or basic mechanical seals
- Installation tolerances are tight; misalignment can lead to premature wear
- Limited temperature range relative to some specialty ceramic‑ceramic seals
Typical Vessels:
TankerBulk CarrierContainer ShipGeneral CargoOffshore Supply VesselCruise Ship
Certifications:
IMO D-2 Type ApprovalDNV GL Type Approval
Decision Guide: Choose if: you need a space‑saving seal for shafts up to 500 mm, have an oil‑lubrication system, and operate at low to medium shaft speeds (≤200 rpm). Avoid if: the propulsion line requires water‑lubricated sealing, operates at high speed, or budget constraints preclude a higher‑cost mechanical seal.
Use Cases: Commonly installed in the stern tube of medium‑speed diesel‑engine driven ships for main propulsion shafts, as well as on auxiliary generator shafts where compactness and low maintenance are priorities.
SKF Simplex Compact C600
unverified
· compact stern tube seal
Seal type
compact stern tube seal
Shaft diameter
600 mm
Application
marine stern tube sealing
Strengths
- Very small axial length – saves valuable stern‑tube space on crowded hulls
- Integrated bearing reduces the need for separate thrust bearings
- Low friction and low power loss compared with larger mechanical seals
- Proven SKF material technology gives good resistance to seawater corrosion
- Standardised mounting simplifies installation and replacement
Weaknesses
- Designed primarily for moderate‑speed vessels; not ideal for high‑speed (>12 kn) applications
- Maximum pressure rating lower than that of full‑size mechanical seals
- Requires regular oil lubrication monitoring to maintain seal performance
- Not suited for extreme temperature or highly aggressive media beyond normal seawater
- Initial purchase price higher than basic lip‑seal solutions
Typical Vessels:
Bulk CarrierContainer ShipGeneral Cargo VesselOffshore Supply VesselSmall to medium Tanker
Certifications:
IMO D-2USCG Type Approval
Decision Guide: Choose if: you need a reliable seal for shafts up to 600 mm where space is limited, vessel operates at moderate speed, and you prefer an integrated bearing solution. Avoid if: the propulsion system runs at high speed or high pressure, requires a heavy‑duty mechanical seal, or operates in unusually hot or chemically aggressive environments.
Use Cases: Commonly installed on new builds and retrofits of medium‑size merchant ships where the stern tube length must be minimised – e.g., bulk carriers or container vessels with single‑screw propulsion. Also used on offshore supply vessels that value easy maintenance and compactness in confined engine room layouts.
SKF Simplex Turbulo T300
unverified
· oil-lubricated turbulo seal
Seal type
turbulo oil-lubricated stern tube seal
Shaft diameter
300 mm
Application
marine stern tube sealing
Strengths
- Continuous oil film reduces friction and wear on the seal faces
- High reliability with low leakage rates even at high shaft speeds
- Long service intervals; compatible with standard SKF bearings
- Simple installation – fits standard stern tube dimensions for 300 mm shafts
- Class‑approved designs available for major classification societies
Weaknesses
- Requires a reliable oil supply and pressure control system
- Sensitive to oil contamination; filtration must be maintained
- Higher initial cost compared with basic water‑lubricated seals
- Not suitable where oil is limited or prohibited (e.g., some environmentally sensitive vessels)
- Installation tolerances are tighter than for simple mechanical seals
Typical Vessels:
Bulk CarrierTankerContainer ShipGeneral Cargo VesselCruise ShipOffshore Support Vessel
Decision Guide: Choose if: you need a proven, low‑leakage seal for shafts up to 300 mm and have an adequate bearing oil system; you value long service intervals and class approval. Avoid if: the vessel operates with limited oil supply, requires a water‑lubricated solution, or budget constraints preclude higher‑cost seals.
Use Cases: Typically installed on new builds or during repowering projects where the propulsion shaft line uses SKF bearings that can feed oil to the seal; common in main propulsion stern tubes of tankers and bulk carriers requiring high reliability and minimal environmental discharge.
SKF Simplex Turbulo T400
unverified
· oil-lubricated turbulo seal
Seal type
turbulo oil-lubricated stern tube seal
Shaft diameter
400 mm
Application
marine stern tube sealing
Strengths
- Proven reliability in high‑pressure marine environments
- Self‑adjusting lip accommodates minor misalignment and shaft wear
- Low friction reduces power loss and shaft heating
- Long service intervals when supplied with clean lubricating oil
Weaknesses
- Requires a dedicated oil supply, filtration and monitoring system
- Potential for oil leakage if the lubrication circuit is not properly maintained
- Higher upfront cost compared with simple mechanical seals
Typical Vessels:
Bulk CarrierOil TankerContainer ShipCruise VesselOffshore Support Vessel
Certifications:
DNV
Decision Guide: Choose if: you need a robust, low‑maintenance seal for shafts up to 400 mm on vessels that already have an oil lubrication system and operate at moderate shaft speeds. Avoid if: the vessel lacks oil supply infrastructure or budget constraints favour a simpler mechanical seal.
Use Cases: The T400 is commonly installed in newbuilds and retrofits of medium‑size merchant ships where reliable stern tube protection is critical, especially on vessels with high service‑life expectations such as tankers and bulk carriers operating in harsh sea conditions.
SKF Simplex Turbulo T500
unverified
· oil‑lubricated turbulo seal
Seal type
turbulo oil-lubricated stern tube seal
Shaft diameter
500 mm
Application
marine stern tube sealing
Strengths
- Provides a constant film of oil, reducing wear and extending seal life on large-diameter shafts.
- Low friction torque loss compared with many mechanical seals.
- Can accommodate slight misalignment and axial movement without leakage.
- Proven track record in marine propulsion applications; compatible with existing SKF oil‑lubrication systems.
Weaknesses
- Requires a dedicated oil supply, filtration and pressure monitoring system.
- Potential for oil leakage if the lubrication circuit fails or is improperly maintained.
- Higher initial cost and installation complexity than dry mechanical seals.
- Maintenance intervals depend on oil quality; contaminated oil can accelerate wear.
Typical Vessels:
TankerContainer shipBulk carrierCruise linerOffshore supply vessel
Decision Guide: Choose the Simplex Turbulo T500 when a vessel already has, or can accommodate, an oil‑lubrication system and needs reliable sealing for shafts around 500 mm with low friction and tolerance to misalignment. Avoid it on vessels where oil supply reliability is questionable, space for additional piping is limited, or where a dry‑run mechanical seal is preferred for simplicity and lower upfront cost.
Use Cases: Typically installed in new‑build or retrofit propulsion systems of large commercial ships, the T500 seals the stern tube of main propeller shafts up to 500 mm, ensuring continuous lubrication during long voyages and harsh sea conditions.
Blohm+Voss
1
Simplex Compact
Per propulsion shaft design
· Seawater / Lube Oil barrier
· compact lip seal
Common Failures & Inspection Points
- Chromium liner scoring
- Seal ring wear
- Oil leakage
- Spring failure
Service: Lip seal type; replace seals at drydock; check chrome liner condition.
Spare Parts: Blohm+Voss: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Compact design reduces overall stern tube length and bearing load on the shaft.
- Integrated spring maintains constant contact pressure, improving seal reliability over a range of operating speeds.
- Chromium liner offers good wear resistance and low friction for medium‑speed shafts.
- Seal rings are designed for straightforward replacement during scheduled dry‑dock periods.
Weaknesses
- Reported scoring of the chromium liner can lead to premature wear if alignment is poor.
- Seal ring material may wear faster than expected in high‑temperature oil environments.
- Spring fatigue has been observed, resulting in loss of sealing pressure and oil leakage.
- Limited to specific shaft diameter ranges; not suitable for very large or high‑power shafts.
Typical Vessels:
Product tankerChemical tankerOffshore supply vesselFerrySmall bulk carrier
Decision Guide: Choose if: you need a space‑saving stern tube seal for medium‑speed vessels, value easy dry‑dock replacement, and operate within the approved shaft size range. Avoid if: the vessel runs at high power or speed, requires ultra‑high reliability in harsh oil temperatures, or if past experience shows recurring liner scoring that cannot be mitigated.
Use Cases: The Simplex Compact is typically installed on medium‑speed merchant ships where space inside the stern tube is limited and regular dry‑dock intervals allow seal replacement. It is common on product tankers and offshore supply vessels that prioritize a compact propulsion layout while maintaining acceptable oil‑tight performance.
Duramax
1
DM Seal 300
Per propulsion shaft design
· Seawater / Lube Oil barrier
· double‑lip mechanical stern tube seal
Common Failures & Inspection Points
- Seal lip degradation
- Shaft liner groove wear
- Aft seal seawater ingress
Service: Duramax lip seal; inspect aft seal at every drydock.
Spare Parts: Duramax: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Robust dual‑lip construction provides redundancy against seal failure
- Corrosion‑resistant elastomer and metal components extend service life in seawater environments
- Standardized dimensions fit a wide range of shaft diameters, simplifying retrofits
- Low maintenance interval; only visual inspection required at each dry‑dock
- Proven track record on medium‑speed propulsion systems
Weaknesses
- Requires precise alignment during installation; misalignment can accelerate wear
- Higher friction torque compared with some oil‑free or magnetic seals
- Aft seal may be prone to seawater ingress if inspection is neglected
- Limited operating temperature range relative to specialty high‑temp seals
- Unit cost higher than basic single‑lip alternatives
Typical Vessels:
TankerBulk CarrierContainer ShipRo‑Ro VesselOffshore Supply Vessel
Decision Guide: Choose if: you need a reliable, low‑maintenance seal for medium‑speed shafts on vessels where dry‑dock inspections are routine and redundancy is valued. Avoid if: the propulsion system operates at very high temperatures or you require an ultra‑low friction solution such as magnetic or oil‑free seals.
Use Cases: The DM Seal 300 is commonly installed in new builds and during major refits of merchant ships with conventional shaft lines, especially where a proven mechanical seal is preferred for its simplicity and ease of inspection.
Kemel
1
KS-3 Marine
Per propulsion shaft design
· Seawater / Lube Oil barrier
· face-type stern tube seal
Common Failures & Inspection Points
- Seal face wear
- Stuffing box leak
- Spring corrosion
Service: Face-type seal; monitor stern tube oil consumption for early leak detection.
Spare Parts: Kemel: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Robust mechanical design with proven service history in merchant vessels
- Straightforward installation and alignment procedures
- Oil consumption can be monitored for early leak detection
- Compatible with a wide range of shaft diameters used on medium‑speed propulsion systems
- Relatively low initial cost compared with more complex oil‑free designs
Weaknesses
- Seal face wear is a common failure mode, requiring periodic inspection and possible re‑grinding or replacement
- Spring corrosion can occur in high‑sulphur or contaminated oil environments
- Oil leakage risk if oil consumption monitoring is not performed diligently
- Limited to conventional shaft line configurations; not suitable for podded or azipod drives
- May require higher maintenance intervals than advanced magnetic or oil‑free seals
Typical Vessels:
Bulk CarrierProduct TankerContainer ShipGeneral Cargo VesselOffshore Supply Vessel
Decision Guide: Choose the KS-3 when you need a reliable, cost‑effective face‑type seal for conventional shaft lines and can implement regular oil‑consumption monitoring. Avoid it if your vessel uses high‑pressure or low‑maintenance oil‑free sealing technologies, operates with highly corrosive lubricants, or requires a podded propulsion arrangement.
Use Cases: The KS-3 is typically installed in the stern tube of conventional shaft‑driven ships during new builds or as a retrofit replacement for aging stuffing boxes. It is favored on vessels where straightforward maintenance and cost considerations outweigh the need for ultra‑low oil consumption or oil‑free operation.
Wärtsilä
1
Airguard 200
Per propulsion shaft design
· Seawater / Lube Oil barrier
· air-operated stern tube seal
Common Failures & Inspection Points
- Seal lip wear
- Air pressure loss
- Oil leakage to sea (environmental!)
- Spring deterioration
Service: Air-type seal; maintain air pressure at 0.2 bar above draught pressure.
Spare Parts: Wärtsilä: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Very low risk of oil leakage to the sea, supporting environmental compliance
- Simple mechanical design with no rotating seals, reducing wear points
- Seal lip can be inspected and replaced without major disassembly, easing maintenance
- Operates on modest air pressure (0.2 bar over draught) and integrates with existing ship air systems
- Proven performance on a range of vessel classes
Weaknesses
- Requires a reliable compressed‑air supply; loss of pressure leads to immediate leakage risk
- Seal lip wear and spring deterioration need regular monitoring and replacement
- Less suitable for very high shaft speeds or highly vibratory installations where the air cushion may be disturbed
- Higher initial purchase cost compared with basic mechanical seals
- Needs precise pressure control equipment and routine checks
Typical Vessels:
Bulk CarrierProduct TankerContainer ShipGeneral Cargo VesselOffshore Support Vessel
Certifications:
DNVABS
Decision Guide: Choose if: you need a reliable low‑leakage seal for medium‑size vessels and have an adequate compressed‑air system; the vessel operates at moderate shaft speeds and environmental compliance is critical. Avoid if: air supply reliability is questionable, the ship has very high shaft speed or extreme vibration, or budget constraints favour simpler mechanical seals.
Use Cases: Typically installed on new builds and retrofits of bulk carriers, product tankers and container ships for main propulsion shafts up to about 10 MW, especially where class societies require low oil discharge. Also used on offshore supply vessels with auxiliary propulsion shafts.