Mobdocks Beat Drydock for Thruster Repair
01 Feb 2003
Antwerp based underwater contractors Hydrex won the SMM/Lloyds List 2002 Award for 'Innovation in Naval Shipbuilding and Marine Technology' last autumn in Hamburg. A significant factor in their victory was the innovative double-Mobdock system, which has again been deployed to repair a container vessel while it was in port loading and unloading its cargo.
The 243m long boxship's thruster tunnel housed a damaged bow thruster which had to be removed from the vessel, sent to the manufacturer for repair, and then later replaced. The double mobdock system was put in place and the six tonne thruster removed while the vessel was in Antwerp on a regular call. The Hydrex team blanked the thruster's hull penetration within the tunnel to the interior of the vessel, enabling it to continue on its normal schedule with extra tug guidance in port.
When the vessel returned to Antwerp a month later, the thruster had been reconditioned and was ready for reinstallation.
The target was again to get the job done within the vessel's normal call time in port. With diver assistance, the first mobdock, which has an 8m access funnel for repair workers, was positioned correctly and secured to the hull of the vessel.
The other mobdock, whose purpose was to seal off the opposite side of the thruster tunnel, was also secured to the hull.
The reconditioned thruster had been placed in the thruster tunnel before operations with the mobdocks began. The blades, disconnected from the thruster, were placed within the mobdock to be connected once the thruster was in position. With the work to be done taking place 10m below the water line, safety procedures were thoroughly checked.
As the thruster was quite heavy, a system to slide it to the centre of the thruster tunnel and then jack it up was devised and fixed in place within the tunnel.
Using this system the thruster was positioned just below the blank hull penetration in the roof of the thruster tunnel where it had to be connected to the E-motor inside the bow thruster room. It was positioned by one part of the team in the thruster tunnel while the other members of the team, within the bow thruster room itself, made the needed connections so that the thruster would function correctly.
After this had been completed, the brackets to support the thruster and prevent it from moving or vibrating in the tunnel were welded onto the thruster so that it was stably in place. The welds were tested and the blades bolted onto the thruster. The area was cleaned, the grids were welded into place at each end of the tunnel thruster and the mobdocks removed.
With the repair team working around the clock in shifts as the vessel completed its cargo operations in port, it was then able to move away from the dock to its normal schedule with minimal tug assistance.
MJ Information No: 17901
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