Are container ships overloaded?
Over the past three months, it is estimated that container ships on the high seas lost over 2500 containers. That is almost twice as many as the average over the past twelve years. Is this a coincidence or is there more to it?
The World Shipping Council, the global interest group for container shipping, proudly reported in July last year that on average around 1400 containers are lost overboard each year worldwide, which is about 0.001 per cent of the total number of containers transported. However, there is a good chance that this average will be substantially exceeded this year, as the Maersk Essen (13,568 TEU) lost some 750 boxes in heavy weather about a fortnight ago in the middle of the Pacific Ocean, about a thousand kilometres north-east of the American atoll Midway.
Remarkably, two similar incidents occurred in November and December of last year, in which an estimated total of some 1850 containers went overboard. The heaviest damage was sustained by the ONE Apus (14,062 TEU) of Japanese Ocean Network Express. At the end of November, in a heavy storm near Hawaii, the ship lost no fewer than 1816 containers, sixteen of which contained hazardous cargo. In addition, many hundreds of containers on board were toppled and photos show that only a few rows of containers remained on deck in the transverse direction. The damage is estimated at at least USD 200 million.
Finally, on New Year’s Eve, Evergreen Marine’s Ever Liberal (8452 TEU) also fell victim to a storm off the coast of Japan, near Kyushu, and 36 containers went into the sea.
The similarity between the two largest container losses is that they both occurred in heavy weather in the middle of the North Pacific Ocean and even relatively close to each other. In addition, the ships are of similar size and were both heavily loaded. Photos and videos of the ONE ship show container stacks toppling over the entire length of the ship and, remarkably, toppling over to both starboard and port side. This indicates that the ship was rolling heavily, tilting alternately to port and starboard, with enormous forces being exerted on the outer container stacks in particular.
In a recent report, the Standard Club, a British insurer, expressed its concern about the increase in scale of the latest generation of container ships, with their capacity of up to 24,000 TEU and width of over sixty metres. This gives them great stability, but the downside is that they roll violently in high waves, resulting in great acceleration forces on ship and cargo. Maersk’s reaction to the container loss of its Essen indicates that the shipping company does not think this is an isolated incident. The shipping company considers it ‘a very serious situation, which will be investigated immediately and thoroughly’.
Although the Maersk Essen and ONE Apus are not ultra-large container vessels, with a length of around 370 metres and a width of around 50 metres they are certainly container giants. Against the background of the peak load in liner shipping over the past six months, there is great commercial pressure to load these types of vessels as full as possible and to sail them as fast as possible, even in heavy weather. According to the Standard Club’s report, such conditions place extreme demands on the twistlocks at the corners of containers used to secure them to each other, as well as on the lashing equipment used to secure them.
Containers are basically fastened together with twistlocks on their four corners. Lashing rods and turnbuckles are then used to secure the container stacks to the deck by connecting them to the ship’s hatches, to special posts on deck or to so-called lashing bridges, if the ship has them. On ships without lashing bridges, only the bottom three layers of containers can be secured with lashing rods, on ships with lashing bridges this is a maximum of five layers. This means that on large modern container ships, the upper layers are only secured with twistlocks.
In addition, the ship’s hull, in combination with the container stacks on deck, acts as a gigantic sail with a length of 360 metres and a height of about 40 metres. This enormous wind force can greatly increase the ship’s movements and further increase the pressure on the container joints and the lashing material. The Standard report also points to a phenomenon known as parametric roll. This can occur if the ship sails straight into the waves or, on the contrary, with them. In certain circumstances, the ship can then come into a form of inherent vibration, which can cause a list of more than thirty degrees. This is not only dangerous for the cargo, it can even lead to loss of the ship.
According to the report, the new very large container ships are more likely to fall into such a state of resonance than smaller ships due to their high stability. A Korean study of parametric roll, published in the Journal of Ocean Engineering and Technology, advocates that ships be slowed down and less heavily loaded. This would greatly reduce the chance of this effect occurring.
Lack of cargo
Commenting on the study, a retired naval architect wrote: ‘The reason why we have not seen many similar accidents in previous years is that most of these large container ships were lightly loaded due to lack of cargo. Now these ships are fully loaded. Therefore, the effect of parametric roll resonance becomes more evident.’
The enormous stability of very large ships also played a role in the container loss of the MSC Zoe (19,224 TEU), which lost at least 345 containers north of the Wadden Islands in the night of 1 to 2 January 2019, an investigation by the Dutch Safety Board and others showed. A huge wreckage on the beaches of Terschelling, Ameland and Schiermonnikoog was the result. This is clearly not the case with the shipping disasters of the Maersk Essen and the ONE Apus on the kilometres-deep Pacific Ocean. In both cases, not a single container was recovered.
Picture: The MSC Zoe lost 345 containers north of the Wadden Islands (by the Netherlands Coast Guard).
This article first appeared in Dutch on Nieuwsblad Transport, a publication of SWZ|Maritime’s publishing partner Promedia.