Napoli incident deemed not a major industry problem

The investigation into the loss of the 4,419 TEU container ship ?MSC Napoli?, which suffered a catastrophic fracture in her hull on 18 January 2007 and had to be beached in Branscombe Bay on the South west coast of England, has identified a number of factors which contributed to the failure of the hull structure.

These included:

? The vessel?s hull did not have sufficient buckling strength in way of the engine room.

? The classification rules applicable at the time of the vessel?s construction did not

require buckling strength calculations to be undertaken beyond the vessel?s amidships area.

? There was no, or insufficient, safety margin between the hull?s design loading and its

ultimate strength.

? The load on the hull was likely to have been increased by whipping effect.

? The ship?s speed was not reduced sufficiently in the heavy seas.

In view of the potential vulnerability of other container ships of a similar design, the UK?s Marine Accident Investigation Branch (MAIB) requested the major classification societies to conduct urgent checks on the buckling strength of a number of ship designs. Over 1,500 ships were screened, of which 12 vessels have been identified as requiring remedial action; a further 10 vessels were identified as being borderline and require more detailed investigation; and the screening of 8 container ships was still in progress at the time of publication.

Remedial action has either been completed, planned, or is being arranged and, where necessary, operational limitations have been agreed or strongly advised until the remedial work has been completed.

Recommendations have been made to the International Association of Classification Societies (IACS), which are intended to increase the requirements for container ship design, consolidate current research into whipping effect, and to initiate research into the development and use of technological aids for measuring hull stresses on container ships.

Recommendations have also been made to the International Chamber of Shipping with the aim of promoting best practice within the container ship industry, and to Zodiac Maritime Agencies, with reference to its safety management system.

In response to MAIB?s request, DNV, the Norwegian class society, and BV, the French class society, conducted a load and strength assessment of the vessel?s hull structure. The objective of the assessment was to provide a probable load range for the vertical bending moment and shear force in way of the forward engine room bulkhead (frame 88) and the corresponding structural hull capacity range.

DNV?s conclusion as a result of its extensive investigation into the MSC Napoli accident in January 2007 is: The accident?s cause is not a general problem for the container shipping industry at large. However, minor structural modifications have to be made to a very restricted number of the existing container ship fleet. Related directly to the MSC Napoli, DNV concluded that the buckling strength in the forward part of the ship?s engine room was less than that of similar vessels. In addition, the newbuilding rules and procedures are being looked at and DNV has invited all members of IACS to cooperate on a unified approach to dealing with the newbuilding rules.

Olav Nortun, DNV Maritime?s technical director, explains: “As the vessel?s class society, our best resources ? both people and cutting-edge computer tools – were put on the job from day one. We?ve left no stone unturned and I?m convinced that this accident and the investigation following it have made the shipping industry even safer.”

The loading caused by the ship itself, its containers and the harsh weather exceeded the capacity of the hull girder and caused the ship to break in half just aft of the forward engine room bulkhead. The critical area was where the longitudinal stiffening of the cargo area ended and the transverse stiffening of the engine room started.

None of the existing container ships classed by DNV has to stop operating. Only two ships have to be strengthened. “This is a minor structural modification which may be done afloat and only involves a small amount of steel,” explains Olav Nortun. “Alternatively, the still water bending moment may be reduced by modifying the loading conditions.”

Based on DNV?s findings, the probability of an accident like that involving the MSC Napoli recurring is very small and the damage statistics for container ships are very good.