The Magazine for Underwater Professionals

Jul/Aug 2016


Seal renewal

Underwater stern tube seal repairs in New Zealand

Hydrex diver preparing to enter mobdock

Earlier this year, a diver/technician team from Belgium-based Hydrex carried out underwater stern tube seal repairs on a container vessel in Tauranga, New Zealand. The ship was suffering from an oil leak and was not allowed to sail on. Because no drydock was available close by, an on-site repair was necessary. Taking advantage of the Hydrex flexible mobdock technique the team was able to carry out the entire operation underwater.

“A leaking seal is always an unpleasant experience for a ship owner,” says Hydrex. “It will force him to go off-hire, costing him time and money.”

To avoid going to drydock and keep the loss of time to the absolute minimum, Hydrex has developed the technology that enables repairs or replacement of all types of shaft seals to be carried out afloat. The ship can keep its schedule as seal repairs can be performed during cargo operations.

“By creating a dry underwater working environment around the shaft, work on the seal assembly can be performed in dry conditions. This is done by using our flexible mobdocks which are designed specifically for this type of repairs. They fit all sizes of seal assembly,” the company says.

Immediately after the New Zealand operation was confirmed, Hydrex’s technical department arranged for a rapid mobilisation of a team of diver/technicians to the container vessel’s location, together with all the needed equipment.


The diving team first set up a monitoring station. The operation then started with a thorough underwater inspection of the stern tube seal assembly. The inspection revealed that the rope guard had gone missing and that the bolts were broken off.

The divers installed the flexible mobdock around the stern tube seal assembly creating a dry underwater environment so that they could work in drydock-like conditions. The split ring was then disconnected and brought to the surface to be cleaned. After cleaning the entire assembly, the team removed the damaged seals one by one and replaced them with new ones.

All parts of the stern tube seal assembly were then reinstalled and secured. Leakage tests were carried out with positive results, after which the divers removed the flexible mobdock.

Every Hydrex office has a fast response centre equipped with all the latest facilities, equipment and tools. “These centres were designed specifically to increase speed of service,” says Hydrex. “The lightweight flexible mobdocks packed in flight containers allow for a very fast mobilisation and a timely arrival of Hydrex teams on any location around the world. This combined with our network of local support bases provides us with everything we need to successfully complete any job, anytime, anywhere.”

  • Reinstalled seal assembly after shaft seal replacement





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