Feature 5 | UNDERWATER MAINTENANCE
Bow thruster repair saves owner time and money
Hydrex carried out the underwater removal and reinstallation of a bow thruster on a container vessel, a process that involved visits to several different ports.
A
s the result of a malfunctioning bow thruster, a 334m long container vessel had to use
the services of a tug boat for port manoeuvring. Consequently Belgium- based Hydrex was contracted to take care of the removal, transportation and reinstallation of the unit. Te operation was performed in stages in several locations to allow the vessel to keep to its sailing schedule. Together with all the necessary
equipment, the Hydrex team travelled to Rotterdam where the operation started with a thorough inspection of the bow thruster unit. One by one the blades were then detached and replaced by blind flanges to prevent oil from leaking from the thruster. Ten the liſting and hoisting equipment that would be used to secure the unit during the second stage of the operation was installed. In the meantime, initial preparations were made 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. Te vessel then leſt for Southampton
where it met up again with the Hydrex team, which immediately 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. Te second part of the operation ended with the installation of a blind flange to seal off the thruster tunnel from the engine room. Te bow thruster unit was then transported to the Hydrex Fast Response Centre by the team and sent on to Norway for repairs. As soon as the overhauled bow thruster gearbox was delivered to the Hydrex
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Hydrex diver-technician climbing out of the water after working in the thruster tunnel.
headquarters, the diver-technician team and the unit were mobilised to the container vessel’s next port of call, Le Havre. Aſter a monitoring station had been set up next to the ship, the team removed the blind flange inside the thruster tunnel. Te unit was then put on a cradle which has been designed by Hydrex especially for bow thruster operations and prevents the unit from tipping. Te cradle can be adjusted to the size of the thruster, and so allowed the Hydrex divers to bring the unit back into the thruster tunnel in one single operation. Due to the size and weight of the bow
thruster unit, special measures were taken to lower the thruster unit and bring it inside the tunnel, where it was repositioned
by using chain blocks. Despite the extra difficulty this entailed, the team was able to reposition the gearbox with only a minimum of delay. Te unit was then secured with bolts, but the chains were kept in place because there was no time leſt to reinstall the brackets before the vessel had to leave for the next port on its schedule. After short vessel stops in Dunkirk
and Hamburg, the team met up with the ship again in Rotterdam, where the chain blocks were removed, following which the propeller blades were reinstalled one by one. To prevent water ingress and oil leaking, the blades were positioned at a ‘6 o’clock’ position instead of the more common and easier ‘12 o’clock’ position.
Shiprepair and Conversion Technology 3rd Quarter 2010
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