Marine Stern Tube Seal
A Blohm+Voss Aegir marine stern tube seal provides a multi‑seal lip arrangement to keep water out of the shaft line while retaining lubricating oil, featuring an aft‑seal oil monitoring port for early detection of seawater ingress.
Inspector Detail
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Common issues
- Lip wear on the aft seal ring allowing seawater ingress
- Air seal pressure loss (on intermediate air-seal designs) allowing oil/water crossover
- Oil leakage past the forward seal into the engine room
- Seawater contamination of lubricating oil, detectable via the aft-seal monitoring port
- Shaft liner scoring reducing seal life
- Loss of header tank pressure/level causing insufficient lip lubrication
Inspection checklist
- Check header tank oil level and top up as needed
- Check the aft-seal monitoring port for water or oil traces
- Inspect air seal supply pressure, if fitted, against maker setting
- Check for leakage at the forward seal housing
- Review oil sample analysis for water content trend
- Confirm shaft liner surface condition where accessible
- Check header tank breather and piping for blockage or damage
Service intervals
| Header tank level / monitoring port check | daily to weekly, per PMS |
| Oil sample analysis | every 3-6 months |
| Header tank oil renewal | annually, or per maker recommendation |
| Seal lip set renewal | typically at drydocking (roughly 2.5-5 years), condition dependent |
Typical wear limits
| Lip seal running surface wear | renew on visible grooving or once leakage exceeds an acceptable drip rate - confirm against maker limits, not a fixed figure |
| Shaft liner wear | assess against class/maker diametral wear tables for the shaft size - no single generic figure applies |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Critical spares
- Complete lip seal ring set (forward/aft)
- O-rings and housing gaskets
- Header tank oil, type as specified by the seal manufacturer
- Air seal element, if an intermediate air-seal design is fitted
- Monitoring port sight glass/sensor
Safety
- Enclosed space entry in the shaft tunnel for inspection/repair
- Pressurised oil/air lines - isolate before opening
- Slip hazard from oil leakage around the seal housing
Class survey
Examined at drydocking/special survey, together with shaft withdrawal or approved in-water survey where applicable; class will look at oil sample records, monitoring port logs and any history of seawater contamination.
Components & Design
Component data being added…
Technical Data
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Common failures & inspection points
Service & Maintenance
Multiple seal arrangement (typically 3-4 seals). Monitor aft seal oil condition for seawater ingress. Drydock seal replacement.
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