South African ship repair company, DORMAC, based in the Port of Durban, has applied its proven ‘C-DAM’ technology to successfully effect a major shell-plate repair to the underside of a container carrier - 10.5 meters below the water-line, without dry-docking the vessel. The ‘Africa Star’, a 17 610-tonne vessel incurred serious damage when colliding with an unknown object when leaving the Port of Cotonou in Benin, West Africa. The vessel continued on her scheduled voyage and on arrival in the Port of Durban, South Africa, called for an assessment of the damage.
DORMAC’s diving team carried out an underwater survey during which varying degrees of damage was observed along a length of 65 metres. Extensive damage was found to 35 square metres of shell plating including a nine metre long tear. Typically, to effect a repair of this nature, the vessel would have had to discharge its entire cargo and proceed to dry–dock. With its ‘C-Dam’ technology, DORMAC was able to put forward an alternative repair proposal, which offered a permanent class-approved repair, without the need to incur these costs.
The cofferdam was constructed in two sections – the main chamber being 15.6 meters long, 3.0 meters wide and with a height of 2.4 meters, and a shaft to provide access for men and materials, which measured 13.6 meters high, 2.4 meters long and with a breadth of 1.5 meters. The total weight of the cofferdam was 36 tonnes. The challenging process of fitting the cofferdam to the vessel commenced with the main chamber. After numerous adjustments, divers were able to confirm the correct positioning through the use of underwater telecommunications with the surface crew. In addition to the contents of the ship’s double bottom, the cofferdam held approximately 120 cubic meters of water, which had to be removed. The next step was to insure that the cofferdam provided the DORMAC steel workers with a safe working environment. An electrical lighting system was installed and 22 safety brackets fitted from the inside of the chamber to further secure the cofferdam to the hull of the vessel. The cofferdam was then ready for a final safety inspection, and on its completion the green light was given to commence with the repair.
Working around the clock, the removal of the damaged shell-plate and associated frameworks and their replacement took just ninety six hours. Quality control involved radiography and magnetic particle inspection and the completed repair was inspected by Germanischer Lloyd. On receipt of their approval as a permanent repair, the new plate was painted, personnel and equipment evacuated and the cofferdam flooded.