Why do serious accidents involving container ships occur again and again at sea? Shipping expert Dieter Becker explains the reasons and shows solutions.
Mr Becker, why are so many containers transported as deck cargo on container ships?
This is related to the so-called "Räumte", i.e. the stowage coefficient of the containers on board a ship. This is the measurement that indicates the cargo hold capacity in cubic metres per tonne of cargo on a ship. Containers only have a stowage coefficient of around 0.40, so they take up a lot of space compared to their weight. As a result, up to 40 per cent of the container volume is transported as deck cargo, stacked up to eight or nine layers high on deck.
How must the containers be secured seaworthy as deck cargo?
The containers are locked at their corners with twistlocks. These then form a stacking tower of up to nine layers, which is exposed to high acceleration forces due to swell in addition to wind pressure and sea impact during sea transport. Secured with twistlocks alone, these container stacking towers can break loose and topple over in a domino effect on deck. For this reason, the containers must also be braced crosswise with lashing rods on container support frames between the individual rows of containers.
So why did so many containers fall overboard on the MSC Zoe?
According to the photographs I have of the MSC Zoe accident, it was not possible to lash the containers properly to the support frames because the support frames were not high enough. Lashing was therefore only technically possible up to the fifth layer. This explains why the upper containers also crashed as a complete package of three as a result of excessive acceleration forces. There are photographs of containers floating together in the sea as a three-pack.
How high are the acceleration forces acting on the upper layers?
They are very high. This has to do with the ever-increasing size of container ships, especially with the width of these ships. The righting stability increases exponentially with the width, improving it so well that this leads to very short rolling times, which means that the acceleration forces in rough seas increase exponentially. The recent container losses have made this clear.
Have lessons been learnt from containers that have gone overboard so far?
According to my findings, yes. In the meantime, there are container giants of more recent construction that have much higher container scaffolding with which the containers can be lashed on deck up to the 7th layer.
What measures do you consider necessary to prevent further accidents?
It would be logical for container ships with insufficient scaffolding height to raise it accordingly and reduce the stacking height until then.
Why do you assume that further container losses are inevitable?
Even today, large container ships are still travelling with support frames that are too low, so I assume that economic reasons prevent the containers from being properly lashed down. The prediction in my report on the MSC Zoe accident has indeed come true very quickly, as on 30 November 2020 the container ship One Apus is said to have lost around 1900 containers on its journey from China to the US West Coast in the Pacific. Here, too, it is noticeable that the container support frames were designed too low, meaning that the upper layers could not be lashed!
Are free and independent shipping experts even needed in this matter?
In my experience so far, no! My comments and expert opinions to the Federal Bureau of Maritime Casualty Investigation (BSU) have not been answered. On the other hand, the Federal Ministry of Transport and Digital Infrastructure (BMVI) has responded to my expert opinion. They thanked me for my comments, but changes can probably only be driven forward via the responsible International Maritime Organisation (IMO). In Germany, the implementation of the BSU's safety recommendations and possible further measures are being discussed in the BMVI's designated expert committees, the Routing Forum and the Cargo Forum. The responsible federal authorities, the federal states and also the associations and experts concerned are represented on this body. My comment on the statement made in the investigation report, "according to which the containers on deck are secured by twistlocks and Lashing rods were secured" (p. 78) and that this is not true in my opinion is included in the cargo forum. I don't believe that I, as a shipping expert, can change anything, at least it's hard to believe, as the accidents continue unabated.
The interview was conducted by Holger Schlüter; images: Dieter Becker
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