Simplex-Compact Stern Tube Seals, Types SC2 and SC3
The SKF Simplex‑Compact SC2/SC3 is a compact stern tube bearing unit that integrates a double‑lip shaft seal with a high‑precision rolling‑element bearing, providing oil‑lubricated support for low‑speed propulsion shafts.
Inspector Detail
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Common issues
- Lip seal wear or hardening over time, leading to oil leakage past the seal
- Oil contamination with seawater if the outer seal fails
- Bearing wear from shaft misalignment or inadequate lubrication
- Corrosion or grooving of the shaft liner running surface under the seal lips
- Sludge or debris build-up in the header tank feeding the seal
- Loss of seal lip spring tension over time
Inspection checklist
- Check header/gravity tank oil level and consumption trend - rising consumption indicates seal wear
- Sample stern tube oil for water content
- Inspect the shaft liner surface for grooving or scoring at the seal running track when accessible (dry-docking)
- Check the seal housing for external oil leakage
- Verify bearing clearance and alignment readings against the maker's tolerances
- Check O-rings and seal lip condition when the unit is opened
- Monitor bearing/seal temperature trend if sensors are fitted
Service intervals
| Stern tube oil sampling (water content check) | typically every 500-1,000 running hours or monthly |
| Header tank level check | daily to weekly, per class requirement |
| Seal lip renewal | condition-based - typically at dry-docking or on leakage/wear evidence |
| Bearing clearance check | at each dry-docking or per the class survey scheme |
Typical wear limits
| Seal lip wear/interference loss | condition-based - renewal is generally recommended when the lip is visibly worn, hardened, or interference loss is evident on inspection; no single numeric limit applies universally - confirm against SKF's inspection guidance for the SC2/SC3 type |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Critical spares
- Complete lip seal set (forward and aft seal rings)
- O-ring/gasket kit for the seal housing
- Bearing shell or liner, if renewal is due
- Shaft liner repair sleeve, if the running track is worn or grooved
Safety
- Loss of stern tube seal integrity can allow seawater ingress into the machinery space or lube oil escape to sea - monitor and report leakage promptly
- Working in the shaft tunnel/stern tube area during running combines confined-space and rotating-machinery hazards
- Environmental/pollution risk from lube oil leakage - report and act per the vessel's SOPEP procedures
Class survey
Stern tube seals and bearings are typically surveyed at each dry-docking or whenever the shaft is drawn or the seal opened for inspection. Class will want oil sampling records, a leakage/consumption trend, and bearing clearance evidence between dockings if the vessel runs an extended tailshaft survey scheme.
Components & Design
Component data being added…
Technical Data
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Common failures & inspection points
Service & Maintenance
Bearing clearance measurement during docking. Shaft seal daily drain inspection. Oil analysis quarterly. Propeller inspection during docking.
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