Shell plate buckling eyed in box ship break up

NOVEMBER 1, 2013 — The ClassNK Casualty Investigation Team looking for the causes of the mid-June incident that saw the containership MOL Comfort break in two has released preliminary findings and safety measure recommendations

The classification society established the team immediately following the loss of the five year old and Japan's Ministry of Land, Infrastructure, Transport and Tourism (MLIT) subsequently established a Committee on Large Container Ship Safety to develop measures to ensure the safety of large container vessels. In addition to its independent investigation, ClassNK is represented on the Committee and is actively involved in its work.

The findings released today are based both on the work of the ClassNK team and the deliberations of the third meeting of the Committee on Large Containership Safety, held on October 28

Preliminary Findings
 
Based on the presence of water-ingress in the bottom of the vessel's midship at the outset of the casualty, the fracture in the vessel's hull is considered to have originated from the bottom part of the vessel.
 
Hull strength and loads at the time of accident were assessed in order to investigate how the fracture occurred and progressed. Structural hull capacity was analyzed using non-linear finite element 3-hold modeling, and dynamic wave loads including whipping effects were also analyzed.
 
Weather, sea state and cargo loading condition data from the vessel's previous voyages are being investigated to estimate the loads acting on the vessel. In addition, structural inspections were conducted on the sister vessels of the MOL Comfort.
 
During the inspections of the sister vessels, buckling type deformations measuring approximately 20 mm in height were observed on the bottom shell plates in the vicinity of center line of midship area. However, it remains unclear at this stage as to whether this type of deformation could have served as a trigger for the casualty. Reinforcement work to increase the hull strength of the sister vessels is already being carried out as a preventative safety measure.
 
With cooperation from shipowners, structural investigations are also being carried out to determine whether similar deformations have occurred in large container vessels with designs differing from those of the MOL Comfort.

Numerical analyses of hull strength and applied loads continue to be conducted in order to develop a more detailed understanding of the casualty and establish countermeasures to prevent the occurrence of similar casualties in the future.

Safety Measures

Based on the preliminary findings noted above, the ClassNK Casualty Investigation Team has proposed the following safety measures be carried out on large containerships in order to prevent the occurrence of similar casualties.  

  • It is recommended that crew inspect the midship section to the extent possible in order to determine whether deformations have occurred on the bottom shell plates. At the request of shipowners, ClassNK will dispatch qualified surveyors to attend such inspections free of charge.
  • If consecutive deformations in the transverse direction are observed on the bottom shell plates a survey is recommended. ClassNK will dispatch qualified surveyors upon request.

Class NK says its team will continue to work closely with the committee as it continues to investigate the MOL Comfort casualty and compile its final report on the incident.