Stern Tube Inspection

Type of project: Inspection and report

Customer Name: UK cruise operator

AtZ Project Engineer: Euan Kelso

Location: Southampton Port, UK

Initial Enquiry:  

AtZ were asked to carry out a stern tube inspection. The vessel had reported leakage from one of their two Wartsila MD stern tube shaft seals of 16 litres per day or more but was unsure if there was likely failure that would require stopping the shaft, or whether the issue could be resolved in service.

The vessel was due to dock within 3 months, and the customer wanted a full and independent evaluation of the condition of both seals, such that they could have required parts available and resolve any issues during repairs.

ATZ has a great deal of propulsion, seal and bearing experience including the design and development of this seal. As such, we were able to offer a thorough and informed assessment of the seal condition to support the customer’s dock plans and support their recommended remedial actions.

Project Objectives: 

Provide independent and expert assessment of the equipment condition within a short time frame from our Southampton base. Make recommendations as to interim measures to be taken on board, and identify parts required for forthcoming refit.

Complete the inspection and report within a single weekend day call in port.

Overcome any unforeseen on-site issues and to the highest standards without delay to the ship’s departure date.

Project Description:  

stern tube service

Vessel had reported an inboard seawater leak from the Starboard shaft. Reported starboard leakage is approximately 16 litres per day. AtZ were asked to attend in order to:

  • Assess the seal condition
  • Recommend any containment actions
  • Advise what future maintenance is required.

System was found to be in satisfactory condition, with air and water supplies correctly configured.

Corrosion of the seal housings, spring assembly and seat were noted. Wear of the rotating seal interfaces was also significant. Evidence of leakage from the port seal was also found.

Monitoring and containment actions were recommended as follows:

Monitor leakage daily to identify any significant changes which may require more urgent intervention. Performance of the port seal was also to be observed.

Regular checks of the inflatable seals to ensure they remained operational in case of emergency.

Inflatable seal operation to be checked and logged monthly by activating the seals when the shaft is stationary. This prevents any excess marine growth build up and checks their condition.

Stern tube replacement


Observed leakage of the starboard and port seal was confirmed, with the most likely source considered to be the worn interface.

Overall condition of the starboard seal required refurbishment in the near future. A major overhaul of the seal assembly to include new interfaces, rubber items, bellows, inflatable as well as re-establishing the seat surface and other corroded surfaces was recommended as a minimum.

The port seal was found to be in a similar condition, and our recommendations therefore apply to both seal installations.

AtZ provided the customer with a thorough and technically detailed independent assessment of their seal condition as well as recommendations for management and repair of observed leakage.

Stern tube overhaul

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