Heavy Lift Dynamics, Sewol Ferry Offshore Salvage

Abstract The Sewol Ferry sank off Korea in 2014 with the loss of 304 lives. The remains of 9 victims remain within wreck and cannot be reached by divers. This paper describes some of the heavy lift engineering involved in the salvage of the 146-meter long ferry, in one piece, from a depth of 44 meters in the ocean, resting on its port side. A method for calculating the interaction of the vessel stern with the seabed (ground reaction) is described as the bow of the 8,000-ton vessel is raised to place lifting beams to be used in the side lift. Significant difficulties, associated with geotechnical issues, resulting in project delays are descried. Calculation methods are presented for determining the large trapped water mass and the large frequency and depth dependent added mass of the submerged vessel (greater than 120,000 tons). Coupled dynamic time domain simulations of the initial bow lift, followed by the side lift onto a floating vessel are presented. A total of 34 HMPE synthetic slings are used to attach a 1,200-ton purpose-built lifting frame to the ZPMC 12,000-ton revolving crane. Wave forecast data from three sources are compared with continuously measured data from a directional wave buoy at the site. The difficulties in predicting and controlling the heel of the vessel with a combination of added buoyancy, slings and geotechnical forces are described for the failed attempt at the first bow lift and for the final bow lift. Dynamic sling tensions are shown calculated for the upper HMPE slings and the lower steel rope vertical and balance slings from the lifting frame to the lifting beams. Detailed static and quasi-dynamic FEA results are described for the Sewol hull, together with buckling checks.