One of larger repair plates is hoisted into position. A thickness of 15mm was used, and the plates were attached using a total of 170 screw dogs. Welding team face a challenge When an 80-metre ship had a nasty encounter with rocks off Boston, a team of specialist underwater contractors travelled from Belgium to make major emergency repairs under difficult circumstances. A number of large gashes to the flat bottom of a container vessel created a major problem for the ship's owner. The damage - from rocks off the US east coast port of Boston - left holes ranging in length from 1 metre to 7 metres. What temporary solution could be provided that would allow the vessel to get across the Atlantic safely to the home repair base in Belgium where the permanent repairs were to be done?     The underwater contracting firm Hydrex was called in to work on the problem and propose solutions for this major repair. Its technical team got together to assess the damage and the extent of work that would be needed; then it worked out ways and means of completing the job.     Repair plans were drawn up in order to obtain the necessary go-ahead from both classification bodies and coastguards for what would be one of the biggest-ever such jobs carried out under water. Trepidation "The plans were sent on to the ship owner," says Antwerp-based Hydrex. "Whilst there was some trepidation about whether such work could be completed by anyone - they were finally convinced that we could do the job." An 8-man team was sent to Boston to start the work with the help of a local company which provided back-up, equipment and consumables. Just to challenge the team further, there were blizzards and freezing weather in the US.     The work required five different patches to be welded to the flat bottom of the ship. The biggest of these was 14.5 metres long by 1.3 metres wide and weighed around 1700 kg. To get this in to position, heavy-duty rigging equipment was necessary and a special procedure needed to be worked out.     To securely attach this and other plates to the ship, the first idea had been to use explosive bolts as part of the system of attachment. However, due to security problems of exporting the necessary tools into the USA, it was not possible to get them through in time.     The team therefore worked out another means of attaching the plates to the ship. "It was done by using a total of 170 screws dogs - an alternative procedure we have for a long time tested and utilised around the world," says Hydrex.     To get all the plates securely attached, an estimated 2 km of underwater weld seams were completed by the Hydrex divers - all of which were qualified and certified underwater welders. These welds were all above-head, as they were made on the flat bottom.     "The plates themselves, while flat on the outside, were designed with two concave surfaces on the inside meeting in the middle," says Hydrex. "This method meant that the inside of the plate would press against the damaged area and increase the surface contact and pressure with the flat bottom, thus ensuring a better contact." Ruptured Seals were, of course, placed all around the contact area, and the empty space behind the plates was filled with concrete in order to stabilise it, prevent vibrations, create an additional seal and, in one case, to prevent the liquids in the fuel tank and the ballast tank mixing as the tear had ruptured the bulkhead between the two spaces.     Due to the extent of the damage, the requirements for the repairs were unusually high. Instead of using the normal 8mm plates, a thickness of 15mm had to be employed throughout.     "This made placement and attachment that much more difficult, but these problems were overcome and finally classification and coastguard authorities not only gave authorisation for the ship to sail back to Europe but also allowed it to be loaded up again."     The temporary repair therefore made it possible for the container cargo to be taken back to Europe.

© 2001 Underwater World Publications Ltd.