On-site Bow Thruster Overhaul Avoids Drydocking

(Press Release)
Wednesday, May 09, 2012

When the bow thruster unit of a 348-meter container vessel needed to be overhauled, Hydrex sent a diver/technician team to the ship to remove the unit on-site and reinstall it again two months later after it had been overhauled. The operation was performed in stages at several locations to allow the vessel to keep to its sailing schedule.

Together with all the necessary equipment, the team first travelled to Rotterdam where the operation started with a thorough inspection of the bow thruster unit. The team then detached the bow thruster blades one by one. In the meantime they made initial preparations in the bow thruster engine room for the removal of the unit, so that there would be no ingress of water once the unit had been taken out. All equipment was then loaded on a Hydrex truck and transported to the vessel’s next stop while the diver/technician team stayed on board the vessel during her voyage from Rotterdam to Le Havre.

Soon after the vessel arrived in Le Havre, the team continued getting the engine room ready. Next the support brackets connecting the gearbox to the thruster tunnel were cut and the unit was secured with chains. It could then be fully disconnected from the thruster room and was carefully lowered, extracted from the tunnel and brought to the surface. The second part of the operation ended with the installation of a blind flange to seal off the thruster tunnel from the engine room to prevent any water ingress during the overhaul period.

Two months later a Hydrex diver/technician team reinstalled the overhauled bow thruster gearbox during the ship’s stop in Valetta, Malta. After the team set up a monitoring station next to the ship, the bow thruster unit was put on a cradle that is designed especially for bow thruster operations and prevents the unit from tipping. As it can be adjusted to the size of the thruster, it allows the Hydrex divers to bring a bow thruster unit back into a thruster tunnel in one take.

The diver/technicians then sealed off the thruster tunnel with the Hydrex flexible mobdocks and emptied all water from it. This created a dry working environment for them in which they could complete the reinstallation of the bow thruster unit in drydock-like conditions.. Next they repositioned the gearbox using chain blocks and secured it with bolts. The thruster propeller blades were then reinstalled one by one. The team completed the operation by reconnecting the thruster unit to the engine room.

After a successful leakage test was carried out, the team removed the flexible mobdocks and flooded the thruster tunnel again. Finally the diver/technicians assisted the vessel’s crew to find the correct pitch for the newly installed bow thruster unit.
By performing both the removal and reinstallation of the bow thruster unit underwater the vessel did not have to go into drydock, saving the owner valuable time and money.

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