Project Specification
Vessel Type: Twin-shaft cruise vessel
Location: Southampton Port, UK
Asset: Twin Wärtsilä MD stern tube shaft seal installations – starboard and port shaft lines
Reported Fault: Confirmed inboard seawater ingress from starboard stern tube shaft seal at approximately 16 litres per day
Time Constraint: Single port call day – all inspection and preliminary assessment completed without delay to vessel departure
Primary Inspection: Scope starboard stern tube seal condition assessment, continued-service risk classification, and dry dock scope definition with parts identification
Fault Report and Inspection Mandate
The operator of a UK cruise vessel contacted MIT Group following confirmed inboard seawater ingress from the starboard stern tube shaft seal installation. The reported leakage rate was approximately 16 litres per day. The operator’s primary question was whether the vessel could continue in service through to its next scheduled dry dock, approximately three months away, or whether immediate shaft stoppage was required. An independent condition assessment was required to answer that question and identify parts for pre-ordering ahead of the planned refit.
MIT initiated the project through its acquisition AtZ (AtZ Martec). AtZ holds significant propulsion, seal, and bearing experience, including involvement in the design and development of the Wärtsilä MD seal. This background enabled MIT to assess wear tolerances, failure mode progression, and overhaul requirements specific to the Wärtsilä MD seal design.
MIT scoped marine project management around the vessel’s available port call window from the outset. The operator required findings and preliminary recommendations before departure.
On-site Stern Tube Seal Inspection
The vessel’s scheduled call at Southampton Port provided a single-day inspection window. MIT Group and AtZ conducted a stern tube seal inspection covering both the starboard and port shaft line installations. Given the nature of the starboard fault, MIT inspected the port Wärtsilä MD stern tube shaft seal in parallel. This was both operationally appropriate and technically necessary.
Inspection Scope
The inspection covered all primary subsystems of each Wärtsilä MD stern tube shaft seal installation. These included the rotating seal interfaces, inflatable emergency seals, spring assembly, seal housing, seal seat surface, and integral air and water supply circuits.
Starboard Shaft Line Findings
MIT confirmed:
- Air and water supply circuits were correctly configured
- Inboard seawater ingress from the stern tube
- Significant wear on the rotating seal interfaces
- Corrosion on the seal housing, spring assembly, and seal seat surface
Port Shaft Line Findings
MIT confirmed:
- Active leakage from the stern tube shaft seal
- The same pattern of rotating seal interface wear and corrosion on the starboard shaft line
As a result, the assessment scope expanded to both installations on equal footing.
MIT documented all findings across both shaft lines within the single port call window. The work had no impact on the vessel’s departure.
Condition Assessment and Risk Classification
MIT concluded that neither shaft line required immediate stoppage. Inspection of both Wärtsilä MD stern tube shaft seal installations identified significant wear on the rotating seal interfaces, consistent with the reported seawater ingress from the starboard shaft. While the wear was advanced, it was progressing gradually and did not indicate imminent seal failure. The inflatable emergency seals remained fully available on both installations.
Corrosion affecting the seal housings, spring assemblies, and seal seat surfaces required remediation during the next scheduled dry dock. However, the condition of the seals and supporting systems presented no acute operational risk within the vessel’s remaining three-month service window.
Both stern tube seal installations required full overhaul at the forthcoming dry dock. The discovery of previously unreported leakage from the port shaft seal reinforced the need to manage both installations under the same monitoring and maintenance programme.
Interim Monitoring and Containment Protocol
To support continued operation until dry dock entry, MIT recommended daily monitoring of leakage rates on both shaft lines, with any increase in leakage triggering immediate reassessment.
The inflatable emergency seals were also scheduled for regular operational checks, including monthly activation with the shaft stationary, to confirm functionality and prevent marine growth accumulation.
Recommended Dry Dock Overhaul Scope
The inspection established a clearly defined overhaul scope for both Wärtsilä MD stern tube shaft seal installations, allowing parts procurement and dry dock planning to begin immediately.
The recommended scope included replacement of all rotating seal interfaces, bellows, inflatable emergency seals, and rubber components, together with restoration of seal seat surfaces and repair or replacement of corroded housing components. The spring assemblies were also identified for detailed assessment during overhaul.
The wear and corrosion observed were consistent with operational age and service conditions rather than any design deficiency within the Wärtsilä MD seal. Drawing on AtZ’s direct experience with the seal’s development, MIT defined a targeted overhaul programme to restore both installations to serviceable condition.
For a directly comparable project involving complete seal and bearing renewal, tail shaft removal, and dry dock execution support, see the Dry Dock Management, Tail Shaft Repair, and Marine Shaft Refurbishment of Chemical Tanker case study.
Need to Arrange an Independent Stern Tube Seal Inspection?
MIT Group provide independent stern tube seal inspections, condition assessments, and dry dock planning support for cruise, passenger, and commercial vessels.
In this case, the team completed a full inspection of both shaft lines during a single Southampton port call, delivering a continued-service assessment, interim monitoring plan, and defined overhaul scope, without impacting the vessel’s schedule.
If your vessel is experiencing stern tube seal leakage or requires an independent assessment before dry dock, contact our team to discuss your next steps.
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