ST Seal
Stop Leak & Water Ingress
The ST Seal product range is designed for different levels of stern tube oil leakage and water Ingress. Core, Plus, and Max are selected based on leakage rate, system condition, oil volume, and operating profile.
System Compatibility & Blending
ST Seal treatments are based on high-quality mineral stern tube oil and are designed to blend with most commonly used mineral stern tube lubricants. The product is added to the relevant oil system according to the recommended dosage and application guidance.
Oil Compatibility Note
ST Seal is intended for selected mineral oil-based systems. For EAL or bio-oil systems, compatibility must be reviewed separately based on oil type, viscosity, additive package, leakage condition, system condition, and operating environment.
Suitable System Types
ST Seal can be considered for aft seal, forward seal, and stern tube applications, as well as common lip seal, face seal / Cedervall-type, air seal, and selected CPP-related sealing arrangements where applicable.
The correct ST Seal variant — Core, Plus, or Max — is recommended based on leakage level, water ingress condition, oil volume, system condition, seal arrangement, and operating profile.
Assessment Before Application
Before treatment, we review the seal type, leakage rate, water contamination level, oil type, viscosity, oil volume, filtration, system configuration, operating conditions, and service objective. This allows us to recommend the most suitable ST Seal variant, dosage, and onboard application approach for the specific case.
ST Seal Product Range
Leakage rates are indicative only. The final recommendation is based on a technical review of the system, seal arrangement, lubricant, oil volume, filtration, and operating conditions.
Application Example
Low-Level Oil Leakage - Fishing Vessel
Vessel type: Fishing vessel
Stern tube volume: ~600 L
Estimated leakage: ~5 L/day
Scenario
During regular fishing operations, the crew observed a consistent low-level oil leakage from the stern tube. The vessel returned frequently to its home port, allowing the crew to monitor the situation over time. While not critical, the leakage showed signs of gradually increasing, raising concern about long-term seal condition.
Action
The operator contacted Addvation to assess the situation. Based on system size and observed leakage, ST Seal Core was recommended as a starting point.
Recommended starting point: ST Seal Core
Indicative quantity: ~40 L total
Application
The product was applied by the crew during routine port stay, following standard application procedures.
Outcome
Leakage was reduced and stabilized, allowing continued operation without further escalation or need for immediate maintenance.
Moderate Oil Leakage - Offshore Vessel
Vessel type: Offshore support vessel
Stern tube volume: ~1,200 L
Estimated leakage: ~15–20 L/day
Scenario
During offshore operations, the vessel experienced increasing stern tube leakage under varying load conditions. The leakage was not constant, but intensified during higher load periods, indicating progressing seal wear.
Action
The operator contacted Addvation to assess the situation ahead of the vessel's next scheduled port call. Based on system size and leakage behavior, a reinforced sealing approach was recommended.
Recommended starting point: ST Seal Plus
Indicative quantity: ~ 70 L total
Application
The product was delivered to the vessel's next port and applied by the crew during port stay, following standard application procedures.
Outcome
Leakage levels were reduced and stabilized across operating conditions, improving system reliability and reducing operational uncertainty.
High Oil Leakage - Container Vessel
Vessel type: Container vessel
Stern tube volume: ~4,500 L
Estimated leakage: ~60–80 L/day
Scenario
During transit, the vessel experienced a significant increase in stern tube leakage, indicating deteriorating seal performance. The leakage level created immediate operational concern, including increased oil consumption and pressure to avoid unplanned dry-docking.
Action
The operator contacted Addvation to assess the situation before the next scheduled port call. Based on system size and leakage severity, a maximum sealing support approach was recommended, with delivery coordinated to the vessel's next port.
Recommended starting point: ST Seal Max
Indicative quantity: ~230 L total
Application
The product was applied by the crew during port stay, following standard application procedures.
Outcome
The issue was resolved to a stable operating level, allowing the vessel to continue as planned - and avoid immediate disruption before planned doc.
Early-stage Water Ingress - Passenger Ferry
Water Ingress – ST Seal Core for a Passenger Ferry
Vessel type: Coastal passenger ferry
Stern tube volume: ~850 L
Observed issue: Early signs of water contamination in the stern tube oil
Scenario
During routine oil checks, the crew observed increased cloudiness in the stern tube lubrication oil. The vessel was operating on a fixed coastal route with frequent starts, stops, and manoeuvring cycles. The system remained stable, but the operator wanted to limit further water contamination and support seal performance until the next planned service window.
Action
The operator contacted Addvation to assess the situation. Based on system volume, oil condition, operating profile, and early signs of water ingress, ST Seal Core was recommended as a starting point.
Recommended starting point: ST Seal Core
Indicative quantity: ~45–60 L total
Application
The product was applied during a scheduled port stay, following the recommended dosage, application guidance, and onboard monitoring procedures.
Outcome
Water ingress was reduced and brought under better control. The oil condition stabilized, allowing the vessel to continue normal operation while the system was monitored toward planned maintenance.
Moderate Water Ingress - Harbour Tug
Water Ingress – ST Seal Plus for a Harbour Tug
Vessel type: Harbour tug
Stern tube volume: ~450 L
Observed issue: Recurring water contamination in the stern tube oil.
Scenario
During harbour operations, the crew observed recurring signs of water contamination in the stern tube oil. The tug operated with frequent manoeuvring, high load changes, and repeated low-speed operation, creating demanding conditions around the seal system. Although the vessel remained operational, the operator wanted to reduce further contamination and avoid immediate intervention.
Action
Addvation reviewed the system volume, oil condition, seal arrangement, operating profile, and observed water ingress. Due to the recurring contamination and demanding operating conditions, ST Seal Plus was recommended.
Recommended starting point: ST Seal Plus
Indicative quantity: ~25–35 L total
Application
The product was applied by the crew during a planned service window in port, following the recommended application guidance and monitoring procedures.
Outcome
Water ingress was reduced and the oil condition became more stable. The vessel continued operation while the system was monitored toward the next planned maintenance opportunity.
Significant Water Ingress - Dredger
Application Scenario
Water Ingress – ST Seal Max for a Dredger
Vessel type: Trailing suction hopper dredger
Stern tube volume: ~1,800 L
Observed issue: High water contamination in stern tube oil
Scenario
During dredging operations in shallow and sediment-heavy waters, the crew observed a clear deterioration in stern tube oil condition. Routine inspections showed increased water contamination, with the oil becoming cloudy and unstable under demanding operating conditions.
Action
The operator contacted Addvation to assess the situation. Due to the harsh operating environment, system size, and water contamination level, a stronger water ingress support approach was recommended.
Recommended starting point: ST Seal Max
Indicative quantity: ~120–150 L total
Application
The product was applied during a planned port stay, following the recommended application guidance and monitoring procedures.
Outcome
Water ingress was reduced and the oil condition became more stable. The vessel was able to continue operation while the system was monitored until the next planned maintenance opportunity.
Why Water Ingress Must Be Taken Seriously
Water ingress can quickly reduce lubrication performance and increase the risk of corrosion, heat, seal wear and bearing damage.
1. Oil contamination
Milky or cloudy oil indicates water contamination and reduced lubrication performance.
2. Corrosion risk
Seawater in the oil can cause corrosion and accelerate internal wear.
3. Heat and friction
Poor lubrication may increase friction, temperature and stress on the seal area.
4. Bearing and seal damage
Untreated water ingress can lead to bearing wear, seal damage and unplanned maintenance.
5. Oil condition before treatment
Light contamination may be treated after assessment. Milky or heavily contaminated oil should normally be replaced before adding ST Seal.
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