The tanker RFA Darkdale was sunk by a German U-boat and was the first British ship sunk south of the equator. She was hit with four torpedoes whilst at anchor off Jamestown, St Helena in October 1941. As she lay in 40 meters depth, her hull is starting to show signs of leaking oil into St Helena .
A team of 9 people from the Ministry of Defence DE&S Salvage and Marine Operations (SANMO) were deployed to St Helena in April to investigate the exact condition of the ship and to ascertain whether RFA Darkdale is likely to become an environmental hazard to the island.
Part of the survey involved using a Tritex Multigauge 4100 ROV mountable thickness gauge, manufactured by Tritex NDT of Dorchester, mounted onto a Seaeye Falcon ROV. The gauge was used to inspect the corrosion levels and determine the amount of wastage that has occurred in the hull and whether there is any risk of the hull leaking any more oil. The Multigauge 4100 uses a technology called multiple echo which means that metal thickness can be easily measured without removing coatings. The multiple echo’s are also compared to each other providing error checked readings from the back wall. The gauge simply mounts onto most types of ROV and is supplied with a datalogging software that allows measurements to be stored in a grid or string format, or a combination of both.
Following the investigation, Mr Andy Liddell, one of the team members, said, “The gauge worked and we got readings off the hull, I have to admit to being surprised given the corroded state of the hull.”
Darkdale RFA was a British Fleet Auxillary Oiler (Dark-Class-Oiler) of 8,145 tons built in 1940 by Blythswood Shipbuilding Co Ltd, Glasgow and owned by The Admiralty (Royal Fleet Auxiliary), London. Previously named Empire Oil. She was torpedoed and sunk on the 22nd October 1941 while anchored off Jamestown Harbour, St. Helena, in the South Atlantic as a storage ship. She was torpedoed by the German submarine U-68.
She was carrying a cargo of 3,000 tons of fuel oil, 850 tons of aviation gasoline, 500 tons of diesel oil and lubricating oil. She was on route from Durban – St.Helena. The Master, Chief Engineer and one member of the crew were ashore. The rest were lost.
[mappress] Subsea World News Staff , July 16, 2012; Image: Tritex