Stern Tube Seal
medium
17 / 17 models (Inspector)
A stern tube seal keeps seawater out of the shaft tunnel and, on oil-lubricated systems, keeps lubricating oil from escaping into the sea - a dual job that makes it the shaft line's single point most likely to cause an environmental incident.
Read more — Stern Tube Seal explained ▾
What defines a stern tube seal
The stern tube seal sits where the propeller shaft exits the hull through the stern tube, and it does two jobs at once: keep seawater from flooding into the shaft tunnel, and, on oil-lubricated stern tube bearings, keep the lubricating oil from escaping into the sea. This second duty is why stern tube seals draw regulatory attention that other shaft line components do not - an oil leak here is a direct pollution event, not just a maintenance concern, and it is the reason environmentally acceptable lubricants and seal monitoring systems have become standard fitment on newer tonnage. Water-lubricated stern tube systems remove the oil pollution risk entirely by running the bearing in seawater, but they trade that for higher bearing wear rates and different seal duty - keeping the bearing supplied with clean water rather than keeping oil contained.
Main components
Forward and aft seal assemblies
Most stern tubes carry seals at both ends of the tube; the aft seal keeps seawater out, the forward seal keeps oil from migrating into the engine room, each typically built from multiple lip seal rings for redundancy.
Sealing rings / lip seals
Synthetic rubber rings running against a wear-resistant liner on the rotating shaft; multiple rings are stacked so a single ring's wear does not immediately result in a leak.
Shaft liner
A replaceable sleeve, historically bronze and increasingly synthetic composite, fitted over the shaft at the seal location so the seal rings run against a renewable wear surface rather than the shaft itself.
Lubricating oil system (oil-lubricated types)
A header tank feeding oil to the stern tube bearing at a pressure slightly above sea pressure, so any leak path runs oil out rather than water in, with oil level monitored as a leak indicator.
Air seal (on some designs)
A compressed air barrier between the forward and aft seal sets on some designs, providing an additional buffer and an early warning if either seal set starts to pass fluid.
Selection and sizing
- Shaft diameter and rotational speed, which determine seal ring size and the surface speed the lip seals must tolerate.
- Lubrication type - oil versus water-lubricated - driven by environmental regulation in the vessel's trading area as much as by mechanical preference.
- Environmentally acceptable lubricant (EAL) compatibility where required by the trading area, since not all seal materials tolerate every EAL formulation equally.
- Draft and immersion depth at the stern tube location, which sets the external sea pressure the seal must hold against.
Regulations and class
MARPOL Annex I addresses oil pollution prevention, and stern tube oil leakage is treated as a reportable discharge if it reaches the sea, which drives most flag states and charterers toward requiring EAL use or leak monitoring in environmentally sensitive areas. US EPA Vessel General Permit requirements specifically call out EAL use in stern tube lubrication for vessels operating in US waters where technically feasible. Class societies require periodic survey of the stern tube seal, typically opened for inspection at the shaft survey interval tied to the vessel's special survey cycle, with continuous monitoring arrangements available to extend that interval where oil condition and seal performance are logged.
Typical faults
| Fault | Cause | Consequence |
|---|---|---|
| Oil leakage into the sea | Worn lip seal rings or liner scoring from a previous seal failure | Pollution event, reportable discharge, potential fine or detention |
| Water ingress into the shaft tunnel | Aft seal failure, often following undetected liner wear | Bilge alarm activation, risk to bearing lubrication if oil is diluted |
| Rising oil consumption without visible leak | Slow seepage past a worn ring, not yet a visible drip | Early indicator often missed until the header tank needs frequent topping |
| Liner scoring | Debris ingress or a seal ring that has already failed and is cutting the liner | Repeated seal failure after replacement unless the liner is also renewed |
What to look for in a supplier
- Seal material confirmed compatible with the lubricant, EAL or mineral oil, actually in use aboard.
- Matched liner supply alongside the seal rings, since fitting new rings against a worn liner shortens the new seal's life sharply.
- Class-recognised type approval for the seal assembly matching the vessel's shaft diameter and speed.
- Monitoring system compatibility if the vessel uses continuous shaft survey arrangements requiring logged seal performance data.
Track oil top-up volume over time, not just oil level at a point in time - a seal that needs topping up more often each month is failing gradually, and that trend line will show it weeks before a visible leak does.
4 manufacturers · 17 models
Wärtsilä
14
Wärtsilä Sandguard
· sand‑protected mechanical stern tube seal
Model Number
Sandguard
Strengths
- Effective protection against sand and debris ingress
- Reduces bearing wear and oil contamination, extending service intervals
- Fits a wide range of shaft diameters and speeds
- Straight‑forward retrofit on existing shafts
- Low routine maintenance compared with conventional lip seals
Weaknesses
- Higher upfront cost than basic lip‑seal solutions
- Requires precise alignment during installation
- Proprietary spare parts can increase replacement lead time
- May be over‑engineered for vessels that never encounter sand‑laden waters
- Limited to shaft speed ranges specified by Wärtsilä
Typical Vessels:
Bulk CarrierOil/TankerContainer ShipOffshore Supply VesselDredgerRiver Barge
Certifications:
DNVGL Type ApprovalABS Classification
Decision Guide: Choose if: the vessel operates in coastal, riverine or offshore areas where sand and fine debris are common, you need to maximise bearing life and minimise unscheduled maintenance, and budget allows a higher initial investment. Avoid if: the ship is a small craft with limited shaft space, operates exclusively in clean‑water environments, or cost sensitivity outweighs the benefit of added protection.
Use Cases: Typically installed on ships that regularly transit shallow, sand‑laden waters—e.g., bulk carriers loading at sandy ports, tankers navigating near coasts, offshore supply vessels servicing rigs, and dredgers where abrasive particles are a constant threat. The Sandguard is also used in retrofits to upgrade older seals that have suffered frequent wear.
Wärtsilä Shaft Line Monitoring Equipment
· shaft line condition monitoring system
Model Number
Shaft Line Monitoring Equipment
Strengths
- Integrated sensor suite delivers temperature, vibration and oil quality data in one package
- Real‑time alarms and trend analysis support condition‑based maintenance and reduce unplanned downtime
- Seamless integration with Wärtsilä ship automation platforms (e.g., Fleet Operations Solution)
- Modular design allows scaling of monitoring points to match vessel size and complexity
- Proven track record on large commercial vessels with extensive field service support
Weaknesses
- Higher upfront capital cost compared with basic mechanical seal alarms
- Installation requires access to shaft line internals and may be complex on retrofits
- Requires trained personnel for data interpretation and system calibration
- Potential for false positives if sensor fouling or wiring issues are not managed
- Limited benefit on small vessels where shaft line loads are low and simple monitoring suffices
Typical Vessels:
Crude oil tankerProduct tankerContainer shipBulk carrierLNG/LPG carrierCruise shipOffshore support vessel
Certifications:
IMO D‑2 (Marine equipment)DNV GL Class approvalABS approved equipment
Decision Guide: Choose if the operator seeks condition‑based maintenance, wants to integrate shaft line health data with existing Wärtsilä automation, and operates vessels where unplanned shaft failures have high cost impact. Avoid if budget constraints dominate, vessel size is small (<5,000 GT), or the fleet already uses a fully compatible monitoring solution from another supplier.
Use Cases: Installed on new builds as part of the ship's condition‑monitoring suite to track seal wear and bearing health; retrofitted on aging tankers and bulk carriers to replace manual temperature gauges and extend maintenance intervals, thereby improving availability and reducing dry‑docking frequency.
Wärtsilä The Seal That Sets a New Standard
· mechanical stern tube seal
Model Number
Navyseal
Strengths
- Very low leakage rates – meets IMO D‑2 requirements for oil containment
- Integrated wear and temperature monitoring reduces unplanned maintenance
- Dual‑lip carbon/ceramic material offers high durability across a wide speed range
- Modular design allows quick installation and replacement on new builds and retrofits
- Compatible with a broad range of shaft diameters and propeller types
Weaknesses
- Higher upfront cost compared with basic lip‑seal solutions
- Requires periodic calibration of the monitoring sensors to maintain accuracy
- Installation space is larger than some compact proprietary seals, limiting use in very tight stern tube arrangements
- Complexity may demand specialised training for maintenance crews
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Supply Vessel
Certifications:
IMO D-2DNV GLABS
Decision Guide: Choose if: you need a high‑reliability seal with proven low leakage, integrated condition monitoring and class approvals for new builds or major retrofits. Avoid if: budget constraints dominate the decision, space in the stern tube is extremely limited, or you lack access to trained personnel for sensor calibration.
Use Cases: The Navyseal is typically installed on modern merchant vessels where environmental compliance (oil spill prevention) and reduced maintenance downtime are priorities – e.g., new‑build tankers complying with IMO D‑2, bulk carriers upgrading to class‑approved seals, and cruise ships seeking continuous monitoring of shaft line health.
Wärtsilä unveils future-proof shaft lines
· Mechanical stern tube seal
Type
Shaft Line Component
Function
Power transmission engine→propeller
Materials
Forged steel + Babbitt
Classification
DNV, LR, ABS, BV
Service Interval
30000 - 60000 h
Approval
IMO oil-pollution prevention compliant
Strengths
- Long service interval (30 000–60 000 h) reduces dry‑dock frequency
- High wear resistance thanks to forged steel and Babbitt lining
- IMO oil‑pollution prevention compliance for environmentally sensitive routes
- Classed by DNV, LR, ABS and BV, facilitating certification on new builds or retrofits
- Designed for easy installation and alignment with Wärtsilä’s shaft line systems
Weaknesses
- Higher upfront capital cost compared with basic rubber lip seals
- Requires specialised maintenance tools and trained personnel for optimal performance
- Spare parts may have longer lead times in remote ports
- Limited to shaft sizes covered by the specific Wärtsilä product range
Typical Vessels:
TankerBulk carrierContainer shipCruise linerOffshore supply vesselLNG carrier
Certifications:
DNVLRABSBVIMO oil‑pollution prevention compliant
Decision Guide: Choose if: you need a high‑reliability seal with long intervals, operate under strict environmental regulations, and have access to Wärtsilä support. Avoid if: budget constraints dominate or the vessel operates in regions where specialised maintenance services are unavailable.
Use Cases: Typically installed on new builds or major retrofits of ocean‑going vessels where shaft line reliability and oil‑spill prevention are critical, such as crude carriers, product tankers, and large passenger ships operating on long voyages.
Wärtsilä Enviroguard MB and M4
· mechanical stern tube seal
Model Number
Enviroguard MB
Strengths
- Oil‑free operation virtually eliminates environmental contamination from shaft seals.
- Integrated temperature and pressure sensors enable real‑time condition monitoring and predictive maintenance.
- Compact design fits a wide range of shaft diameters (typically 150 mm to 300 mm).
- Low friction reduces power loss and extends bearing life.
- Designed for easy installation and quick replacement during scheduled dry‑dock.
Weaknesses
- Higher upfront capital cost compared with traditional gland‑packing seals.
- Requires precise shaft alignment and surface finish; tolerances are tighter than for packing.
- Limited to vessels where the propulsion system can accommodate the seal’s hydraulic pressure supply.
- Replacement parts and service must be sourced from authorised Wärtsilä dealers, potentially increasing lead time.
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Supply Vessel
Decision Guide: Choose if: you need to meet strict environmental regulations on oil leakage, want integrated condition monitoring, and are building a new vessel or undertaking a major retrofit where shaft alignment can be verified. Avoid if: budget constraints dominate the project, the existing shaft geometry cannot meet the tighter tolerances, or the vessel operates with limited hydraulic pressure availability.
Use Cases: The Enviroguard MB/M4 is commonly installed on new builds and during major dry‑dock overhauls of merchant ships where low emissions are a priority, such as double‑hull tankers and eco‑focused bulk carriers. It is also favoured for offshore support vessels that operate in sensitive marine areas requiring minimal oil discharge.
Wärtsilä oil lubricated stern tube seals
· oil lubricated stern tube seal
Model Number
Wartsila Oil Lubricated Seals
Strengths
- Integrated bearing lubrication reduces separate oil circuits
- Proven reliability in high‑power propulsion applications
- Low friction and wear rates extend service intervals
- Straightforward installation with standard Wärtsilä fittings
Weaknesses
- Requires a dedicated oil supply and filtration system
- Performance degrades if oil becomes contaminated or low in level
- Higher initial cost compared with basic mechanical seals
- Limited temperature range relative to some ceramic‑based alternatives
Typical Vessels:
TankersBulk carriersContainer shipsCruise linersOffshore support vessels
Decision Guide: Choose if: the vessel operates at high shaft power, needs integrated bearing lubrication, and can accommodate an oil supply system. Avoid if: a low‑maintenance mechanical seal is preferred or oil handling infrastructure is limited.
Use Cases: Deployed on the main propulsion line of large commercial ships where continuous oil lubrication of the stern tube reduces wear and prevents water ingress, especially in vessels with Wärtsilä engines and bearing systems.
Wärtsilä Enviroguard M Seal
· Mechanical shaft line seal
Model Number
Enviroguard M
Strengths
- Oil‑free sealing eliminates lubrication losses and reduces environmental discharge.
- Very low leakage rates compared with traditional packing (typically <0.5 L/h).
- Modular design allows easy installation and replacement on a wide range of shaft diameters.
- Integrated condition monitoring options enable early detection of wear or misalignment.
Weaknesses
- Higher initial capital cost than conventional packed gland solutions.
- Requires precise alignment and may need auxiliary cooling for high‑power applications.
- Replacement parts and specialised service can be more expensive and less widely available in remote ports.
Typical Vessels:
TankerBulk CarrierContainer ShipCruise ShipOffshore Supply Vessel
Decision Guide: Choose if: you need low‑leakage, oil‑free operation for environmental compliance and are building new vessels or undertaking major refits where the higher upfront cost can be justified. Avoid if: budget constraints dominate, the vessel uses low‑speed shafts that can tolerate traditional packing, or service facilities for mechanical seals are unavailable in your operating area.
Use Cases: The Enviroguard M is typically installed on new builds and major retrofits of merchant ships where stern‑tube leakage control and emission reduction are required—e.g., modern tankers complying with IMO MARPOL Annex VI, cruise liners seeking reduced oil discharge, and offshore vessels needing reliable long‑term sealing for high‑speed shafts.
Wärtsilä Sternguard E Series seals
· Mechanical stern tube seal
Model Number
Sternguard E
Strengths
- Very low leakage rates even at high pressure differentials
- Integrated bearing reduces separate bearing inventory and alignment work
- Oil‑lubricated carbon ring gives long service intervals and good wear resistance
- Compact design fits in limited stern‑tube spaces on modern vessels
- Proven track record on a wide range of vessel classes
Weaknesses
- Higher upfront cost compared with simple lip seals or gland packs
- Requires a dedicated oil supply and filtration system; contamination can cause premature wear
- Installation and replacement typically need dry‑docking, increasing downtime
- Maximum shaft speed limited (generally <200 rpm) for optimal performance
- Complexity of monitoring wear may require additional instrumentation
Typical Vessels:
TankerLNG/LPG carrierOffshore support vesselCruise shipContainer shipBulk carrier
Certifications:
DNV GL Type ApprovalABS
Decision Guide: Choose if: you need a reliable, low‑leakage seal for high‑pressure applications and have the oil supply infrastructure; space constraints favor a compact integrated design. Avoid if: budget is extremely tight, shaft speed exceeds the seal’s rating, or you prefer a quick‑change simple pack that can be serviced without dry‑docking.
Use Cases: The Sternguard E is typically installed on vessels with high‑power propeller shafts where leakage of lubricating oil into the sea must be minimised – e.g., tankers carrying hazardous cargoes, LNG carriers with cryogenic systems, and offshore supply ships that operate in environmentally sensitive waters.
Wärtsilä Sternguard In-water serviceable seal
· In-water serviceable mechanical stern tube seal
Model Number
Sternguard In
Strengths
- Allows on‑board servicing without dry‑dock, reducing vessel downtime
- Double‑lip design provides low leakage rates and high reliability
- Compatible with a wide range of shaft diameters and speeds
- Straightforward installation and alignment procedures
- Class‑approved by major societies (e.g., DNV‑GL, ABS)
Weaknesses
- Higher upfront capital cost compared with basic lip seals
- Requires trained personnel to perform in‑service maintenance correctly
- Oil consumption must be monitored; improper servicing can lead to wear
- Limited to vessels where shaft speed and pressure are within design limits
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Supply Vessel
Certifications:
DNV‑GL Class ApprovalABS Class Approval
Decision Guide: Choose if: vessel operates on long voyages or high‑availability schedules where dry‑dock intervals must be minimized, and the operator can support skilled in‑service seal maintenance. Avoid if: budget constraints dominate or the ship’s propulsion system is low‑speed/simple where a basic seal suffices.
Use Cases: Typically installed on main propulsion shafts of large commercial ships that require high availability—e.g., tankers crossing oceans, bulk carriers on continuous trade routes, and cruise ships with tight schedule commitments. The seal enables routine lubrication or minor repairs while the vessel is underway, extending intervals between dry‑dockings.
Wärtsilä EvoTube®
· Mechanical stern tube seal
Model Number
EvoTube
Strengths
- Dual‑lip design gives high pressure resistance and minimal leakage
- Low wear rate reduces maintenance intervals and downtime
- Integrated condition‑monitoring sensors enable predictive maintenance
- Broad size range fits many shaft diameters and speeds
- Designed for harsh marine environments with temperature‑stable materials
Weaknesses
- Higher initial purchase price compared with conventional lip seals
- Requires precise alignment and installation tolerances
- May need a dedicated lubrication system for optimal performance
- Replacement can be more complex than simple packing seals
- Limited to vessels that can accommodate its axial length
Typical Vessels:
Oil TankerLNG CarrierBulk CarrierContainer ShipCruise ShipOffshore Supply Vessel
Decision Guide: Choose if: you need a high‑reliability seal with low maintenance, operate in temperature‑extreme or high‑pressure conditions, and can invest in the upfront cost. Avoid if: budget constraints dominate, existing shaft geometry cannot meet alignment requirements, or a simpler, lower‑cost packing seal is sufficient.
Use Cases: Commonly installed on new builds for main propulsion shafts where leakage tolerance is critical—e.g., oil tankers, LNG carriers, and cruise ships—and also used in retrofits to replace aging lip seals with a more durable solution.
Wärtsilä Enviroguard PSE seal
· Polymer mechanical stern tube seal
Model Number
Enviroguard PSE
Strengths
- Very low oil leakage – helps meet strict emission regulations
- Compact, lightweight design simplifies installation and retrofits
- Wide operating range (rpm, pressure) suitable for most merchant vessels
- Long service intervals due to wear‑resistant polymer elements
- Compatible with a variety of shaft line lubricants
Weaknesses
- Maximum allowable shaft speed lower than high‑performance metal seals (~3 000 rpm)
- Polymer faces can be more sensitive to abrasive particles in seawater
- Requires precise alignment during installation to avoid premature wear
- Higher upfront cost compared with simple lip‑seal solutions
- Limited temperature range relative to all‑metal sealing systems
Typical Vessels:
Oil TankerBulk CarrierContainer ShipGeneral Cargo VesselOffshore Supply Vessel
Decision Guide: Choose if: you need a low‑leakage, environmentally friendly seal for vessels operating at moderate shaft speeds and want easy installation or retrofit. Avoid if: the propulsion system runs at very high rpm, operates in highly abrasive water conditions, or budget constraints demand the cheapest possible seal.
Use Cases: The Enviroguard PSE is commonly installed on new builds and during mid‑life upgrades of merchant ships where compliance with IMO pollution standards is a priority. It is favoured for vessels that run diesel engines or dual‑fuel units where oil leakage from the stern tube must be minimised, such as tankers transporting clean petroleum products.
Wärtsilä water lubricated stern tube seals
· water-lubricated stern tube seal
Model Number
Wartsila Water Lubricated Seals
Strengths
- Zero oil leakage – eliminates environmental risk from seal oil discharge
- Reduced routine maintenance (no oil changes or seal oil replenishment)
- Integrated condition monitoring compatible with Wärtsilä propulsion control systems
- Lower operating cost over the life‑cycle due to absence of oil handling and disposal
- Compact design that can be fitted on new builds or retrofitted onto existing shaft lines
Weaknesses
- Requires high‑quality seawater filtration and temperature control to avoid corrosion and cavitation
- Limited to certain shaft speed/power ranges (typically up to ~200 rpm, medium‑power applications)
- Higher upfront capital cost compared with conventional oil‑lubricated mechanical seals
- Potential for increased wear if water quality is not maintained within specifications
- Additional auxiliary equipment needed (filters, cooling loop, monitoring sensors)
Typical Vessels:
Bulk CarrierOil TankerContainer ShipCruise ShipOffshore Support Vessel
Certifications:
DNVGL Type Approval
Decision Guide: Choose if: you need an oil‑free sealing solution to meet strict environmental regulations, operate vessels with Wärtsilä main engines that already use seawater cooling, and can provide reliable water filtration. Avoid if: the shaft runs at very high speed or power beyond the seal’s design envelope, budget constraints prohibit higher initial investment, or the vessel lacks infrastructure for water treatment and monitoring.
Use Cases: Commonly installed on new builds and retrofits where MARPOL Annex VI or class society requirements demand zero oil discharge from stern tubes. Used on medium‑speed vessels (10–15 kW per meter of shaft) such as bulk carriers, tankers and cruise ships to reduce maintenance workload and environmental impact while integrating with Wärtsilä’s engine monitoring systems.
Wärtsilä intermediate shaft bearings
· intermediate shaft bearing with integrated seal
Model Number
Wartsila Intermediate Shaft Bearings
Strengths
- High load capacity and low friction design suitable for a wide range of propeller sizes
- Integrated condition monitoring (vibration/temperature) reduces unplanned downtime
- Modular construction simplifies installation and replacement during dry‑dock periods
- Proven reliability on Wärtsilä engine platforms with extensive field service history
- Compatible with standard lubrication systems and offers optional oil‑free variants
Weaknesses
- Higher purchase price compared with generic off‑the‑shelf bearing solutions
- Spare parts and service support are primarily through Wärtsilä networks, which may limit availability in remote ports
- Installation requires specific alignment tools and trained personnel
- Weight is greater than some lightweight aluminium alternatives, affecting overall shaft line mass budget
- Proprietary design can restrict use with non‑Wärtsilä propulsion arrangements
Typical Vessels:
Bulk CarrierTankerContainer ShipCruise VesselOffshore Supply Vessel
Certifications:
DNV
Decision Guide: Choose if: you operate a medium‑speed diesel engine on a Wärtsilä platform, need high reliability and integrated condition monitoring, and can accommodate the higher upfront cost. Avoid if: budget constraints dominate, you require a bearing compatible with multiple engine manufacturers, or you need rapid spare‑part availability in regions without Wärtsilä service presence.
Use Cases: These bearings are typically installed on newbuilds and major retrofits where the intermediate shaft links a Wärtsilä main engine to the propeller. They are common on vessels that run long voyages with high propulsion loads, such as bulk carriers and tankers, where minimizing unplanned shaft line failures is critical.
Simplex Compact Seal
Shaft diameter 200-1000mm
· Propulsion Shaft Line
· Lip seal stern tube
Type
Lip Seal Stern Tube
Common Failures & Inspection Points
- Lip seal wear causing oil leakage
- Chromium liner scoring
- Air seal chamber pressure loss
- Spring tension loss
Service: Monitor stern tube oil consumption for seal wear. Replace seals at drydock. Check chromium liner for scoring. MARPOL — zero discharge target.
Spare Parts: Wärtsilä (Cedervall): Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Compact design saves space in the stern tube arrangement
- Integrated air chamber reduces oil leakage and supports MARPOL zero‑discharge goals
- Spring‑loaded lip provides consistent sealing pressure over a range of shaft speeds
- Relatively easy to install and replace during dry‑dock periods
- Compatible with standard chromium liners used on many vessel classes
Weaknesses
- Lip wear can lead to oil leakage if not monitored; requires regular inspection
- Chromium liner may be scored by the lip seal over time, increasing maintenance
- Spring tension loss reduces sealing effectiveness and must be checked periodically
- Limited to certain shaft diameter ranges; not suitable for very large or high‑speed shafts without engineering review
- Air‑seal chamber pressure loss can occur if installation tolerances are not met
Typical Vessels:
Bulk CarrierOil TankerContainer ShipGeneral Cargo VesselOffshore Supply Vessel
Decision Guide: Choose if: you need a space‑saving stern tube seal with low oil consumption, you operate vessels subject to MARPOL zero‑discharge requirements, and the shaft size falls within the Simplex Compact range. Avoid if: the vessel uses very high shaft speeds or diameters outside the approved range, or if you prefer a full‑air‑seal system that does not rely on a lip element.
Use Cases: The seal is typically installed in the stern tube of merchant ships during new builds or retrofits where space constraints and oil‑leakage control are priorities. It is common on bulk carriers, tankers and container vessels that require class‑approved sealing solutions and aim to meet strict environmental discharge limits.
Blohm+Voss (Aegir)
1
Marine Stern Tube Seal
Shaft diameter 150-800mm
· Propulsion Shaft Line
· Multi-seal lip system
Type
Lip Seal Stern Tube
Common Failures & Inspection Points
- Seal lip wear
- Air seal pressure fluctuation
- Liner surface damage
- Aft seal oil contamination with seawater
Service: Multiple seal arrangement (typically 3-4 seals). Monitor aft seal oil condition for seawater ingress. Drydock seal replacement.
Spare Parts: Blohm+Voss (Aegir): Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Four‑seal configuration offers redundancy and high reliability
- Aft seal oil sampling point enables proactive detection of seawater contamination
- Robust liner material reduces wear and extends service intervals
- Standardized dimensions facilitate retrofit on existing shafts
- Proven track record on long‑haul ocean vessels
Weaknesses
- Installation is complex and requires experienced personnel
- Higher upfront cost compared with single‑seal solutions
- Requires regular monitoring of aft seal oil condition
- Lip wear can increase under very high RPM or abrasive conditions
- Spare parts may have longer lead times due to specialized design
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Support Vessel
Decision Guide: Choose if you need high‑reliability, redundant sealing for large propulsion shafts and have the capability to monitor aft seal oil condition. Avoid on small vessels or low‑budget projects where a simpler single‑seal system would suffice.
Use Cases: Installed on the main propulsion shaft line of ocean‑going commercial ships during drydock periods; commonly used where long service intervals and protection against seawater ingress are critical, such as in tankers, bulk carriers, and cruise liners.
Duramax Marine
1
ROMOR Water-Lubricated Bearing
Shaft diameter 75-1000mm
· Propulsion Shaft Line
· water-lubricated stern tube bearing
Type
Water-Lubricated Stern Tube Bearing
Common Failures & Inspection Points
- Bearing surface wear
- Shaft sleeve corrosion
- Debris ingestion damage
Service: EPA VGP compliant (no oil). Composite material — excellent shock resistance. Monitor clearances via poker gauge.
Spare Parts: Duramax Marine: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Oil‑free operation meets EPA VGP regulations, eliminating oil handling costs and environmental risk
- Composite material offers superior shock absorption and corrosion resistance compared with metal bearings
- Clearance can be monitored directly with a poker gauge, simplifying routine inspections
- Reduced maintenance intervals in clean water environments due to lack of oil degradation
Weaknesses
- Bearing surface wear can accelerate if water quality is poor or debris ingress occurs
- Shaft sleeve corrosion may develop when operating in high‑salinity or low‑oxygen water without adequate cathodic protection
- Requires robust filtration and regular debris checks to prevent damage from foreign material
- Performance may be limited in very low‑speed applications where oil‑lubricated bearings provide better damping
Typical Vessels:
Bulk CarrierContainer ShipGeneral CargoOffshore Supply VesselFerry
Decision Guide: Choose if: you need an oil‑free, environmentally compliant stern tube solution on vessels operating in relatively clean seawater and value shock resistance. Avoid if: the vessel frequently runs in high‑debris or highly corrosive water where metal bearings with proven cathodic protection are preferred.
Use Cases: Commonly installed on mid‑size merchant ships and offshore support vessels that operate in regulated waters, where eliminating oil handling simplifies compliance and reduces spill risk. Often selected for retrofits where existing shaft lines can accommodate a composite sleeve and where maintenance crews favor direct clearance checks.
Thordon Bearings
1
SXL Water-Lubricated Bearing
Shaft diameter 100-900mm
· Propulsion Shaft Line
· Water-lubricated stern tube bearing
Type
Water-Lubricated Stern Tube Bearing
Common Failures & Inspection Points
- Bearing stave wear
- Shaft sleeve erosion from sediment
- Water flow restriction
- Alignment issues
Service: Seawater-lubricated — zero pollution risk (EPA VGP compliant). Monitor bearing clearances. Replace staves when clearance exceeds limit.
Spare Parts: Thordon Bearings: Dichtungs-Elemente und Verschleißmesswerkzeuge an Bord vorhalten. Lead time: 4-8 Wochen.
Strengths
- Zero oil discharge – fully compliant with environmental regulations (EPA VGP).
- Simplified maintenance – no oil changes or disposal required.
- Corrosion‑resistant materials designed for long service in seawater environments.
- Lower operating cost when clean seawater is readily available.
Weaknesses
- Higher susceptibility to wear if sediment or debris enters the water flow.
- Requires strict alignment and regular clearance monitoring; misalignment accelerates stave wear.
- Load capacity generally lower than comparable oil‑lubricated bearings, limiting use on very high‑power shafts.
- Performance degrades in low‑flow or highly turbulent water conditions.
Typical Vessels:
Bulk CarrierOil/TankerContainer ShipGeneral CargoOffshore Supply Vessel
Decision Guide: Choose if: you need an environmentally‑friendly bearing, operate in vessels where seawater is clean and abundant, and shaft loads are within the medium range. Avoid if: the vessel runs in high‑sediment waters, requires maximum load capacity, or cannot guarantee precise alignment and regular clearance checks.
Use Cases: Commonly installed in the stern tube of merchant ships to support propeller shafts where oil‑lubricated bearings would pose a pollution risk; especially favored on vessels operating under strict emission regulations or in regions with stringent ballast water standards.