Why and How Did the MOL Comfort Break in Half? Structural Flaw or Improper Loading?

mloc4Why and how did the MOL Comfort break in half? The obvious answer is that no one knows, yet. We will learn more following an investigation, which is many months in the future.  In the mean time, what are the likely causes of such a casualty?  How and why could an only five year old ship, delivered in 2008, built at good quality shipyard, Nagasaki Shipyard & Engine Works, operated by a well known and established ship owner, Mitsui O.S.K. Lines, simply break in half?

The how is easier to answer right now than the why. From the photographs immediately after the ship began to crack, it appears that the hull failed due to excessive longitudinal bending stress. Container ships typically operate with a certain amount of bending stress due to the difference between the downward load of the weight of the cargo and the upward thrust of the buoyancy of the water. The downward load is distributed more evenly along the length of the container ship while the upward buoyancy is more concentrated toward the middle of the ship. Most container ships sail with a moderate amount of hog, which is to say with a slight downward droop in the bow and stern due to the imbalanced load. This is only noticeable when taking the draft of the ship at her marks forward, amidships and aft. Otherwise it is effectively invisible. The bending stress only increases as a ship works in a seaway. Ships, of course, are designed to handle these stresses, which is what makes the break up of the MOL Comfort such a shock.

So what could cause such a catastrophic failure? The two most obvious answers are a structural flaw in the ship’s hull girder or improper loading of container cargo. The first alternative, a structural flaw caused by improper design or fabrication, is not unheard but is highly unusual in a new ship. It has happened before with older ships.

MSC Carla

MSC Carla

In 1997, for example the MSC Carla, a 25 year old ship sailed from La Havre bound for Boston and broke in half roughly amidships, off the Azores. The ship had been lengthen in 1984 and the failure was at the forward end of the new midbody. The design and installation of the new structure by the shipyard, Hyundai, was found to have been faulty.

While a structural flaw could be explanation for the MOL Comfort breaking in half, it seems to me much more likely that the ship was improperly loaded. Traditionally, the first concern in loading a container ship was stability, for obvious reasons. One glance at containers stacked 6 and 7 high on deck of a typical large container ship makes it clear why it is important to keep the heavier containers low so the ship does not roll over. Stability is generally well monitored and planned for. It is also obvious if you get it wrong. In addition to using loading programs to perform stability calculations, a captain can judge the stability of his ship by simply timing the roll period in a swell. If a mistake has been made, it should be evident.

Longitudinal strength is not quite as easy. For many years, longitudinal strength wasn’t a concern in most general cargo ships, including most early container ships. As ships grew longer and larger, however, mates an stevedores had to consider the ship’s longitudinal strength alongside the ship’s stability. Now, just as they have had to be very careful in the cargo’s center of gravity for stability, they also have to take care that they do not load too much weight in the ends of the ship, particularly on deck, so that the bending stresses will remain with within allowable limits. Fortunately, loading programs now allow the mates and stevedores to calculate longitudinal strength.

But how could have things gone so wrong on the MOL Comfort? If the cargo was loaded improperly how did it happen? One of the best and worst aspects of container ship operation is that the ships do not spend much time in port. Cargo handling is quick and efficient and a ship can be back to sea in hours rather than days or even weeks as was the case in the days of breakbulk cargo ships. If a ship in port for eight hours for example that doesn’t leave much time to for the Chief Mate to properly study the loading plan as he attends to other duties. Properly loading an 8,000 TEU ship like the MOL Comfort is immensely complicated. Multiple port calls also adds to the complexity. Container ships do not simply load in one port, cross an ocean and discharge in another. When the MOL Comfort sailed from Jeddah she had been calling multiple ports, loading and discharging containers along the way. If the containers loaded at Jeddah happened to be loaded toward the ends of the ship, and the ship had enough stability, it is possible that she sailed with a higher than acceptable bending stresses.

This is all speculation on my part. Nevertheless, improper loading seems a potentially cause for the catastrophic hull failure on the MOL Comfort. The failure could indeed have been caused by a structural flaw, or even by the combination of a structural flaw and improper loading. That being said, I wouldn’t be at all surprised if the failure was due to improper loading alone. Given the constraints and the operating tempo of container ship operation,it is not a particularly surprising mistake to have seen made. If this does turn out to be the case, we will see far more attention paid to calculation longitudinal strength when loading container ships in the future.

Comments

Why and How Did the MOL Comfort Break in Half? Structural Flaw or Improper Loading? — 24 Comments

  1. Good analysis as always. What I can’t understand is why some enterprising tug-operators haven’t gone after the two sections-the salvage claim would be enormous!

  2. Could the hogging have been caused by flooding of a compartment in the bow section?

  3. in case of bulk carrier i agree it can break into two halves. but in case of container ship it is not digestible. main strength of ship is torsion box which run from forward to aft longitudinally and in this box formed structure high tensile steel is used. so how such type of incident takes place?

  4. Container ships can be improperly loaded so that their allowable longitudinal bending stress is exceeded. I know this because I have worked through container loading plans and have seen that it is not that difficult to stress the ship beyond the allowable limits.

    High tensile steel can almost make the problem worse in that while the steel has a higher allowable stress, it has the same deflection as mild steel. It can result in a very “bendy” ship. This can accelerate cracking around structural details which never would have been a problem with mild steel.

  5. I will tell you why MOL Comfort was “disabled” but you will not believe me. Regardless if you believe or not, this truth will be made known very soon.

    Cargo on board included military arms and weapons for the Syrian rebel force, which is, in fact, a covert U.S. govt. operation with the goal to destabilize the Syrian govt. and cause a war.

    This war will not be allowed to happen. That is why MOL Comfort was broken into two pieces. The military arms and weapons were not allowed to reach Jeddah.

    Who did this? ETs (extraterrestrials) who are helping humanity at this time.

    You will not believe this but it is the truth and you will find out for yourselves very soon.

  6. It’s consistent with timing of all other political moves in respect to Syria that this shipment contained larger military supply destined for US-backed rebels/FSA.

    Such structural failure could easily be achieved with a deep-detonated torpedo, breaking the ship by the pressure/displacement wave.

    http://www.dailymail.co.uk/news/article-2188791/Russian-attack-submarine-slipped-past-US-Navy-patrolled-Gulf-Mexico-weeks-undetected.html

    All in all, a good result for the balances of power. No need to worry about construction or loading. Just move on.

  7. If loading was a factor, it is not new. The OCL Liverpool Bay class of ships, with a 40ft hatch in front of the bridge, caused immense headaches to stowage planners in the 1970s, due to the necessity to have really heavy 40fts both below deck and on deck in that hatch. On hte other hand, the Ben Line equivalents had twin 20ft stowage in front of the bridge and the stresses and hogging were far less of a problem. This was long before the mammoth vessels today. You could stand on deck aft, and look forward to see the vessels hogging, without even reading the draft marks.
    The other issue is whether there was too much sheer stress on the bulkhead, with too much heavy weight on one side and little weight on the other side.

  8. Thanks for mentioning sheer loading. More of a problem in the multipurpose bulkers but could also play a role on a containership as well. And you are right. There is nothing new with loading problems on container ships.

    Thanks for the comment.

  9. The fact that both halves are still at even keel makes me carefully conclude that the containers stowed fore and aft should be empty ones.Such a loading condition could hardly cause severe hogging moments.It is doubtful whether the failure started with progressive buckling of the double bottom members or has it been caused by abundant use of ultra high strength steel in the topsides.
    Moreover the longitudinal distribution of maximum permissible bending moments – at the so-called readout points of the loading computer is accuretely defined and calculated by the shipyard and verified by the class.However,the calculation of the actual distribution of bending moments requires an accurate input of all deadweight items i.e container weights, water ballast , fuel etc.
    The question remains whether the crew has been properly provided with the right values of these items .

  10. The forward section of the ship has a trim by the head. The good news is that because both sections are still afloat the calculations will be able to be run and compared directly to the ship as loaded.

  11. MOL Comfort has a bit smaller sister ships known s E-Class.
    This is Panamax container vessels. I used to work on MOL Expeditor which is presently in service.This vessel being 2 years old had already cracks in structures in vicinity of cargo hold No.2 visible in under deck passageway.Management was aware about this but did not do nothing. At least that time. Probably MOL Comfort had same problem of construction.

  12. High tensile steel because it is harder than mild steel, case hardens and crystallizes faster. Improper preventive maintenance to X Ray all the welds and bearing structures then replace sections that have crystallized costs a fortune, as well takes time costing further money because it is not hauling freight. Preventive maintenance to the propulsion and navigation systems was in all probability a much higher priority than the true money generating structure of the hull itself.
    The amount of scum and mariene crustation visable in the exposed ballast compartment is further evidence of neglect to the hull on the part of the owner. A 5 yr old ship run to death for profit, insurance on the ship on the cargo will make up the price of the next one they will run to death.
    Torsion box structures fail, as the world saw in the collapse of both towers of the world trade centers, after there construction in high wind they could sway more than a foot. Once the integrity is compromised a torsion box is doomed.