THE INVESTIGATIVE report released by Japan’s ClassNK into the catastrophic loss of the container ship MOL Comfort — one of the largest ships ever lost at sea — raises some worrying issues for the industry as a whole.
In particular, it highlights one of the oft-neglected truths of container ship sizes getting ever larger — the bigger the vessel, the bigger the mess when something goes wrong.
It is important to grasp the context of the investigative report, because while it is essential the maritime industry learns the causes of such a disaster, at the same time there are vested interests at play as various parties seek financial redress for the loss.
To recap on the main facts of the accident, the 2008-built, 8100-TEU MOL Comfort was constructed at the Mitsubishi Heavy Industries Nagasaki shipyard in Japan in 2008.
On June 17,2013, she suffered a crack amidships in bad weather about 200 nautical miles off the coast of Yemen, en route from Singapore to Jeddah, with a cargo of 4382 containers (both 20ft and 40ft units equivalent to 7041 TEUs).The crew of 26 abandoned the ship and were rescued from two life rafts and a lifeboat by another vessel. The MOL Comfort broke into two, with both sections remaining afloat. The aft section sank on June 27 and the bow section, after having been destroyed by fire, on July 11.
Early this month, the Japanese classification society ClassNK (which classed MOL Comfort) issued its report having been tasked by Japan’s Ministry of Land, Infrastructure, Transport and Tourism to find out the cause of the disaster.
It suggested it could have been due to a ship:specific issue (ie not a generic flaw among container ship design) relating to excessive lateral loads such as bottom sea pressure and container weights.
Specifically, the loads on the ship could have exceeded the hull girder ultimate strength, when taking into account uncertain factors such as the difference between declared and actual container weights and stormy sea conditions.
MOL Comfort was a “very rare” casualty that split and sank due to rough weather conditions and “problematic” vessel operation and management, it said.
That appears a fairly blunt assessment but in fact ClassNK had to be circumspect because litigation is under way between Mitsubishi. Heavy Industries (MHI), the vessel owner and operator MOL and cargo and insurance interests.
Under Japan’s Product Liability Law, MOL is seeking at least US$131.6 million from MHI for alleged negligence and defects in the container ship. MHI has rejected any responsibility for the incident, saying MOL Comfort’s design and construction complied fully with class rules.
It is also worth mentioning that the all-Japanese nature of the investigation drew some criticism, with fellow class society DNV GL saying it would have been better to have technical collaboration on an international scale. On face value, however, the investigation appears thorough.
A panel led by the class society investigated over 17 container ships ranging in size between 6000-8000 TEUs, seven of which were subjected to elasto-plastic analyses (a means of measuring loads and stress on a structure, which was deemed to reproduce the actual condition of the ships more precisely).
When calculating by the International Association of Classification Societies’ method, which does not consider the effect of lateral loads such as bottom sea pressure and container weights, the panel observed all vessels met the requirements in relation to vertical bending strength.
However, when using elasto-plastic analyses, the investigation found a significant difference between MOL Comfort and other vessels in hull girder ultimate strength against wave -induced vertical bending.Inspections found no deformation like that which existed in the bottom shell plates of sister ships of the MOL Comfort.
There are other, wider impacts on the industry to consider in relation to the investigation findings. One is that it found post-Panamax container ships face more risks due to their lesser need to ballast.
Larger container ships are generally more stable, because they have more cargo on board, and therefore do not need to ballast in their double-bottom tanks as often. According to the report “the minimisation of ballast increases the frequency with which the still water vertical bending moment reaches close to the allowable value”.
In lay person-speak, I take that to mean the larger ships can face structural stresses that possibly havenot been fully recognised up to now. Given the trend for ships to get larger and larger, this is an important safety issue for the industry to solve.
To counter this, ClassNK has called for ship designers to take various loading conditions into account. It is also going to review its own in-house miles, which could possibly lead to the development of methods to better assess hull strength with consideration of lateral loads via elasto-plastic analyses.
The trend for ships to get larger — leading to the increasing size of vessels coming to small countries like New Zealand — also brings with it the stark fact that when an accident does happen, the consequences are likely to be far worse than other disasters we have encountered.
The Rena was only a 3032-TEU vessel, which is a common-enough size in New Zealand trades but is just a feeder size in many bluewater trades. She was about 2500 TEUs smaller than the largest container vessel to come in New Zealand.
She was carrying only 1368 containers, not a large load at all. As mentioned earlier, the MOL Comfort was of 8100-TEUs capacity with a cargo of 4382 containers equivalent to 7041 TEUs.
The saving grace, in terms of environmental damage, was that the MOL Comfort went down 200 nautical miles off the coast of Yemen, whereas the Rena was in sight of beaches.
The Rena experience also shone a light on the practical difficulties that salvors face in recovering cargo, fuel and the hull itself when a large vessel founders.
This was discussed earlier this year by the International Salvage Union and respected Lloyds List commentator Michael Grey, at one time a mariner on the New Zealand trades. He asked the question: “How on earth can you lighten a ship with containers up to 10 high on deck and 24 across?”
There are only about 80 barge mounted offshore cranes in the world capable of lifting at that height.
As for the industry problem of misreporting the manifested weights of containers, which may have been a factor in the MOL Comfort tragedy, this is an issue which has been tracked closely by this column over the years, and at last is indeed being tackled by the industry.
The concluding comment of Michael Grey was there are dangers inherent in carrying our cargo “eggs” in ever-bigger baskets.
To that, I’d add another metaphor — the bigger they are, the harder they are going to fall.