The South African Navy has succeeded in bringing Tug de Mist to the surface after it sank in shallow water in Simon’s Town harbour last month.
Navy spokesman, Commander Greyling van den Berg, said the vessel was successfully salvaged on Thursday December 6 after several days of hard work.
He said operations commenced after a comprehensive assessment was conducted by the naval engineering department and the navy divers.
The salvage entailed raising the tug off the seabed and towing it to the synchrolift facility about 50 metres away.
However, he said, shallow water salvages are known to be extremely difficult because of the lack of air expansion and buoyancy at this depth.
The main challenge experienced over the last few weeks, he said, was trying to make the 39-year-old tug airtight and buoyant.
The divers used underwater welding equipment to seal off holes in order to pump it full of air, but as soon as leaks were sealed, other leaks bubbled to the surface but with the help of the staff at Armscor Dockyard, this was resolved.
He said on Wednesday November 28, the navy divers concentrated all lifting efforts to the aft of the tug, managing to raise it and bring it two metres away from the quay, with its keel resting on the bedrock.
The same was achieved on the forward side and the Mooring Lighter, built by dockyard apprentices more than 100 years ago, was used as mechanism to create further lift. Because of the tug’s age, he said, the Mooring Lighter does not have a generator and cannot operate its capstan. In order to mitigate this, the winch of Tug Umalusi was used to create this lift through the Mooring Lighter’s fair leads.
He said the docking plate under the tug kept getting stuck in the sand during the lifting process, adding to complications and throughout the lifting process, divers continued sealing off leaks and filling fuel, freshwater and ballast tanks with air.
Commander Van den Berg said on Monday December 3, the naval riggers in conjunction with the naval harbour master, devised a way of using “snatch blocks” to create further buoyancy.
The aim was to raise the tug high enough to clear the platform of the synchrolift which was achieved on Wednesday December 5.
The prevailing airlocks in the tug, however, created balance issues, which were finally overcome around midnight on that evening.
Floating, but still listing slightly, the tug was finally pulled to the synchrolift.
“The salvage operation and obstacles overcome is an amazing display of teamwork and resourcefulness by the dedicated team of professionals who worked tirelessly to solve numerous mathematical, physical and engineering problems,” Commander Van den Berg said.