The Magazine for Underwater Professionals
Unique Seaflex buoyancy key in salvage of historic WW2 landing craft
Unique Seaflex (Seaflex), UK, a division of Unique Maritime Group, UAE, has played a key role in the refloating of the only surviving landing craft from D-Day 1944.
Working in conjunction with Salvesen UK, Seaflex deployed 230 tonnes of buoyancy from its office in the Isle of Wight to the operation in Birkenhead Docks, Liverpool, UK.
Ian McDonald, dive supervisor at Salvesen UK, says: “Without the great help from Unique Seaflex this project would not have been possible, and whilst we recognise that there are other lift bag suppliers in the UK, our choice is made for us on this and other projects by the quality of Seaflex equipment and the professionalism and expertise displayed by their staff.”
Ben Board, technical site support manager at Unique Seaflex, says: “It was a great honour to work with Salvesen on such a prestigious UK heritage project. Whilst we have since diversified into other buoyancy applications for the offshore industry, we built our business on this type of salvage work and it is very much in our own heritage.”
The project to lift and save LCT 7074 began in March 2014, almost four years to the day after she had sunk. The vessel came out of service at the end of World War Two after numerous successful deployments to the Normandy beaches; she was converted to a naval repair facility for a short while, then became a floating nightclub, and was berthed in Liverpool from around 1950.
Salvesen UK, an established Liverpool-based contractor that conducts more than 1000 diving projects a year, was engaged by Comet Technical Services, UK, on behalf of the National Museum of the Royal Navy to conduct a dive survey and some NDT inspection of the vessel during March 2014, the result of which was that the hull was deemed in good enough condition to attempt the refloat. A grant of nearly GB£1 million was awarded by the UK National Memorial Heritage Fund and operations recommenced in September 2014.
After three weeks of diving to clean the vessel and prepare her for internal diving operations, the landing craft was ready to be refloated. Although for salvage operations open-ended parachute-style air lift bags are generally preferred, this was one of those jobs where a combination of the relatively shallow depths and the need to squeeze buoyancy into tight spaces meant that enclosed units fitted with pressure release valves were the ideal solution. A significant number of such enclosed units as well as parachute-type lift bags are held by Unique Seaflex within its rental pool for near-immediate despatch and just-in-time delivery by Unique Seaflex for such projects.
Salvesen began by installing 18 five-tonne single-connection vertical Unique Seaflex mono buoyancy units (MBU) into the wing tanks, which run fore and aft, port and starboard. The contractor then burnt holes either side of the vertical frames in the wing tank bulkheads to secure a further 20 five-tonne MBUs. As these units would break the surface before the vessel was fully afloat, the full lift potential of 190 tonnes would not be achieved, but it would be supplemented by eight five-tonne multiple-connection horizontal inflatable buoyancy units in the main engine room. Salvesen then successfully and safely tunnelled under the vessel’s approximate 10 metres’ beam, creating a 1.5-square-metre aperture to allow two 100-tonne soft slings to be inserted; these were then restrained and connected to two spreader beams.
A floating crane was then mobilised to assist with the lift, initially loaded to 50 tonnes. The lifting bags were then inflated sequentially so as to provide a stable and as controlled lift as possible with the stresses on the vessel being monitored throughout by digital strain gauges at various locations on the hull. With all the bags inflated, the load on the crane was increased at five tonne increments, and at 105 tonnes on the crane the vessel slowly began to rise from the seabed. After the tank deck level was reached, approximately 400,000 litres of water was pumped out and the vessel was successfully refloated. All the salvage equipment was then removed from the hull and final preparations made for her transfer to Portsmouth Naval Base for restoration.