Sewol ferry disaster

MARIN’s engagement with the Sewol goes back to early 2018. MARIN was one of the major contractors of the Sewol Investigation Commission and throughout the first half of 2018 conducted model tests and simulations to find the cause of the Sewol’s capsizing and sinking.

TURNING AND HEELING

To analyse the capsizing and flooding, a 6 meter long free-floating model (9929) was built equipped with working screws, rudders and stabilizing fins. The sliding containers, cars and trucks were also modeled. For turning and heeling, MARIN tested more than 340 scenarios combining different conditions of speed, stability, cargo movement, rudder movements, and fin stabilizers. We also conducted tests on the potential impact of 'external force' on the ship’s turning and heeling.

According to MARIN’s analysis, the combination of low stability and rudder movement caused the ship to heel at least 18 degrees to the port while turning to the starboard, at which point the cargo started to shift. When the ship heeled 33 degrees after the initial cargo movement, the second cargo shift occurred and the Sewol ended up heeling more than 45 degrees and did not recover its position.

FLOODING AND SINKING

Subsequently, tests were carried out with a 5 m long model (9930) in which all compartments, tanks and inflow openings were accurately recreated to scale to investigate the flooding and sinking. The analysis showed where the initial water intake occurred and how the flooding progressed. In particular, MARIN’s simulation showed that, if its watertight doors and manholes had been closed properly, the Sewol would not have sunken as quickly as it did.

main conlusions

March 2020, during the Sustainable and Safe Passenger Ships conference organised by RINA, MARIN submitted two papers on 'Heel Angles in Turn and Passenger Safety' and 'Sewol Ferry Capsizing and Flooding', presenting the main conclusions:

  • Stability of SEWOL was lacking (conversion, cargo, tanks, trim)
  • Rudder excursion occured (helmsman, steering gear)
  • Fast Turn with Large Heel (>18 degr.)
  • Cargo ( not properly secured ), slided at 18 and 33 degr. heel
  • The heeling increased to 45 degr.
  • Water ingressed via scuppers and vent at C deck
  • Water flowed through vent pipe into stabilisation room and E.R.
  • Due to water on C deck, ferry capsized and flooded fast

IMO

The International Maritime Organization (IMO) Intact Stability regulations for passenger ships adopted in 2008 provide a formula with which to calculate the heel angle from several characteristics of the ship. According to the rule, the heel angle in a turn calculated with this formula cannot exceed 10 degrees. In the stability range provided by the SIC and tested by MARIN, the Sewol did not meet that IMO formula, so it is not surprising that the Sewol heeled more than 10 degrees during the accident.
MARIN proposes that, because we cannot check the actual maximum heel angle with the current formula, the IMO should specify the maximum heel angle of 15 degrees, around which passengers physically lose their balance, and adopt a new formula to verify it. MARIN prepared a proposal for revision to the Maritime Safety Committee of the IMO.