At the core of the new technique is what is called a 'flexible mobdock'. This new type of mobdock is made of extremely durable, but supple lightweight material. It is fixed with a watertight seal around the thruster tunnel, or area being worked on, with a gap at the bottom for access into the work space. These mobdocks are applied to both ends of the tunnel or open areas of the work space and air is then pumped into the tunnel itself, forcing the water out and thereby creating a dry area within the tunnel where work can be done.

This particular method is suitable for all work that does not require access inside the ship through the area being worked in. For work requiring internal access, the traditionally constructed steel Hydrex mobdocks are necessary for safety purposes. However, for this particular job, the work that had to be done consisted only of the removal of propeller blades and then the renewal of the seals.

Once the flexible mobdocks had been put in place and the dry area created within the thruster tunnel, the Hydrex work team was able to enter the tunnel itself and construct a block and tackle that was hung from the top of the thruster tunnel. With this in place, the first blade was unbolted from the propeller hub and moved out of the way so that access to the hub itself was made easy. It was then a matter of cleaning out the seal and replacing the faulty O-ring with a new one and then securing the blade back in place. This operation was repeated for each of the seals of the remaining three propeller blades.

The hub was then tested for further leaks and once found to be in top condition, the flexible mobdocks were removed and the ship was able to start its cruise on schedule.

The great advantage of this new method is that it is not necessary to construct large steel mobdock structures, which takes time and money. This technology has been developed to a new stage and can be easily applied anywhere in the world with a minimal amount of personnel and equipment. It is therefore an extremely fast and economical way of dealing with a variety of problems such as oil leaks or blade damage. The savings of both time and money compared with putting the ship into dry dock can be substantial.

MJ Information No: 20324