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For years cofferdams (called mobdocks in Hydrex ter- minology - short for 'mobile mini dry docks') have need- ed to be large metallic structures that make a watertight fit to the hull of a vessel in order to seal out water from the area being repaired. Hydrex has pioneered many different uses of mobdocks including sealing off thruster tunnels at both ends, removing the water and creating a dry space within. This enabled specialists to perform repairs or even change thrusters whilst the vessel was carrying out port activities such loading or unloading, without all the added time and problems connected to going into dry dock.

The first mobdocks for thruster tunnels were initially large, specially shaped, metal structures that fitted to the curved hull around the thruster tunnel. In many cases, this is now no longer needed. Hydrex has broken new ground in the last year and come up with a 'flexible mob- dock' allowing diver-technicians to work within the thruster tunnel. Once the water has been removed, tech- nicians can work within the thruster tunnel. The cost of producing heavy metal structures is usually no longer needed, which in turn means time saved on the repairs.

Rene Huybreghts, General Manager of Hydrex, said "The flexible mobdocks are the latest result of a fast serv- ice we have been looking to achieve for years. We have already done a number of jobs using them last year and now they are into full operation with several jobs done this month. They open up a whole new dimension to pro- vide better service in the field of underwater ship repairs."

One of the jobs, done in Portsmouth, U.K., was the removal and replacement of a bow thruster gearbox. A flexible mobdock was installed and all water was removed from the tunnel. In this 'dry environment' underwater, the propeller blades were first removed from the hub. The gearbox and electromotor were then dismounted and dis- 40 MTR May 2006

Flexible Mobdocks Make their Mark diving

Hydrex diver working underwater. Overhauled thrusters unloaded.

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