Napoli – Time To Box Clever

Some container industry executives might have been asking “Where’s the love?” when the UK’s Maritime Accident Investigation Branch report on the structural failure of the MSC Napoli landed on their desks this week, most, however would have had an inkling that a rap on the knuckles was in sight.

MSC Napoli was beached in Branscombe Bay, Dorset, by its master after a crack appeared in its hull by way of the engine room during a storm. Analysis showed a weakness in that part of the hull that went undetected because measurements of resistance to buckling were only taken in an area amidships of four tenths of her length overall, which did not include the engine room and which was the only area required to be checked by the classification society rules.

It was not a problem of fatigue or corrosion, but inherent in the design. Typically, a ship structure will maintain much the same configuration along its length, as frames diminish in size towards the bow and stern they effectively match the reduced global bending loads along the length of the ship away from the midships area. In the MSC Napoli, however, the structure was changed from longitudinal to transverse a little fore of the engine room, where stresses were almost as great as at amidships, but the structure itself was weak under the sort of compressive loading the vessel experienced.

A later survey of 1,500 similar vessels, with input from classification societies, discovered another 12 ships with similar problems that needed immediate attention and another 10 which required further investigation. Data on another eight ships had yet to be provided by the classification society concerned.

MAIB comments: “the commercial advantages of containerisation and intermodalism such as speed and quick turnarounds appear to have become the focus of the industry at the expense of the safe operation of its vessels. The industry is very schedule driven, and operators inevitably have an eye on the timetable when making key decisions.”

The MSC Napoli report identifies:”…the decisions to: sail without an operational governor; sail in excess of the maximum permissible seagoing bending moments in order to allow greater flexibility for
the time of departure; to operate at near maximum bending moments when underway; and to keep the ship’s speed as fast as possible when pounding into heavy seas, were symptomatic of the industry’s ethos to carry as much as possible as quickly as possible. However, although these decisions were undoubtedly made in the belief that the ship was operating within acceptable limits, this investigation has shown that unknown variables such as whipping effect and container weights are able to erode or
eliminate the safety margins in place.”

Containerships, with long, relatively narrow designs, are particularly subject to the effects of bending moments in rough seas and the ‘whipping effect’, which can typically increase wave bending
moments on container ships from between 10 per cent and 50 per cent. Any increase in the wave
bending moment above the normal design level would inevitably erode the margin between loading and hull strength. However, MAIB points out : “it is apparent that whipping effect is currently very difficult to reliably calculate or model. Classification societies are therefore unable to predict its magnitude or effect on a ship’s structure, with any confidence, and as a consequence they are not generally calculated during the structural design process.”

Basically, safety margins may be far smaller than accounted for. Indeed, the increase in the size of containerships has outpaced the regulatory environment. Says MAIB: “At the time of build, no buckling checks were required by the applicable rules, and none were made. However, as the current
requirements specified in UR S11 leaves buckling checks outside the 0.4L amidships region to the discretion of individual classification societies, there is a possibility that even if MSC Napoli had been built after 1992, the lack of buckling strength in way of her engine room would still not have been identified. Importantly, it is highly probable that there are a number of other container ships of a similar design to MSC Napoli which are also vulnerable to localised buckling in severe conditions. It is essential that such designs are quickly identified and remedial action is taken where necessary”

Buckling strength, says MAIB must be measured globally, along the length of the ship, not just the .4 of a ships length amidships. This was less important for yesterday’s shorter vessels: It’s easy to break a full-length matchstick, but harder to snap shorter lengths, for instance. A single common method for establishing buckling strength is vital for today’s containerships.

How soon is that likely to happen? Lloyd’s List quotes IACS principal technical officer Colin Wright “We always respond to MAIB recommendations and they have sent out a message that says please get on with it. It is already in hand, though when it will be finished is another matter,” he said. Not, prehaps, the most exciting of responses.

“No ship is unbreakable. Classification societies apply structural strength limitations which are contingent on the application of good seamanship and prudent operational practice. It has been apparent during the course of this investigation that these caveats are not widely recognised by many in the container ship industry. Unlike other large vessels such as bulk carriers, which can frequently disregard the effect of the sea, due to their lines and limited engine power, container ships cannot. It is essential that companies recognise this difference and put in place controls and procedures to ensure that container ships operate within safe limits at all times,” says the MAIB report.

There were, however, other safety issues raised in the report that were related to container operations. Calculations showed a great discrepancy between declared container weights and their actual weights, which might not have directly led to the hull failure but would have contributed to the reduction of the safety margin between the total bending moment experienced and the strength of the hull. Without accurately weighing containers, the stresses on the hull cannot be accurately predicted.

Perhaps surprisingly, there is no dedicated trade organisation for the containershipping industry to provide guidance on best practices. In its report on the collapse of containers on the Annabella, MAIB commented “Working practices relating to the planning, loading, transportation and discharge of containers are largely unregulated and have been understandably focussed on the need to maximise efficiency and speed of operation. While key industry players will attest that safety is of paramount
concern, evidence obtained during this and other MAIB investigations into container shipping accidents suggests that in reality, the safety of ships, crews and the environment is being compromised by the overriding desire to maintain established schedules or optimise port turn round times.”

In response, the International Chamber of Shipping has convened a group of container ship industry experts and, with the assistance of the World Shipping Council, has started work to develop and publish a code of best practice for the industry. The code is expected to be completed by the end of 2008, after which it will be presented to IMO for adoption.

The Maritime And Coastguard Agency has added inspections of container weight and ship longitudinal strength checks on containerships to its paper to the Paris MOU Port State Control Subcommittee on the subject of operational checks and the human factor in loading of ships and whether adequate checks were being carried out prior to sailing. The UK will lead a task force to consider these checks for a concentrated inspection campaign planned for 2010, taking into account the findings of the MSC Napoli report.

The message from MAIB to the industry is clear: Get your act together, or, at least, learn to box clever.

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