[Answer] How Are Underwater Bow Thruster Operations Performed?


An article published in Maritime Technology explains the operation of underwater bow thruster in Oslo.

About the Incident

A team of Hydrex diver/technicians were mobilized to Oslo, Norway for an underwater bow thruster operation on a large ferry. A seal in the gearbox was leaking and needed to be replaced.

A small window was made available for the operation, but the repair had to be finished before the next scheduled trip.

Tailor-made cofferdam

A preliminary inspection of the bow thruster had revealed the cause of the leak.

After studying the information, the Hydrex technical department proposed to replace the defective seal underwater with a tailor-made cofferdam.

This cofferdam was designed by the company’s R&D department and fabricated at their headquarters in Antwerp.

Rectification process

One of the Hydrex teams then traveled to Oslo with their truck and all the required equipment. After arriving on site, they set up a monitoring station next to the ferry.

The cofferdam was then brought into the thruster tunnel, positioned over the gearbox and secured. This allowed the divers to remove the water from the cofferdam.

As a result, a dry working environment was created around the gearbox for the Hydrex technicians to work in.

The team then safely removed the thruster case cap. This gave them access to the damaged seal ring, which they replaced with a new one to conclude the repair part of the operation.

All that needed to be done was to fully reassemble the gearbox and remove the cofferdam.


  • Flexibility is an important element of every job Hydrex carries out, but in this case it was crucial that the repair was finished before the ferry needed to depart with its passengers.
  • Taking into account the scope of the job this was not an easy accomplishment. The team worked in shifts throughout the entire operation. Hydrex adapted the operation to the schedule of the ship without losing the safety and quality standards that the company imposes on any job they perform.

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Source: Maritime Technology