The probable causes of the MOL Comfort accident with respect to vibration

Please Note that this is completely my determination. The actual cause may not be this. 

Introduction

 On The 17 June 2013 a modern 8,110 TEU container ship the MOL Comfort built in

2008 by MHI Nagasaki Shipyard split into two halves while on transit from Singapore to

Jeddah (Saudi Arabia). All 26 crew, consisting of 11 Russians, 1 Ukrainian and 14 Filipinos,

escaped the sinking ship on two life rafts and a lifeboat. The stern section containing

approximately 1,500tonnes of fuel oil sank on 27 June and the fore part which was being towed

by a salvage company sank on 11 July 2013 having been partly destroyed by fire. [1]

The real reason of the incident is still unknown. In this report, I would like to give my opinion

regarding the cause of the incident.

Figure 1 : MOL Comfort Incident

MOL Comfort Vessel Particulars

Table – 1: Vessel Particulars [2]

Cause of the Incident (Schematic)

Cause of the Incident (Detailed Description)

    On June 17, 2013 MOL Comfort was on transit from Singapore to Jeddah (Saudi

Arabia). The real reason of the MOL Comfort incident is still unknown. However, I would like

to provide my opinion on the incident. I think, during transit it was experiencing hogging and

sagging. Which led the vessel to face lateral and vertical bending loads. As a result, hydroelastic

effects were induced. Hydroelasticity is the interaction of hydrodynamic and elastic

structural forces which led to vibration of floating and submerged ocean structures/vessels. It

is believed that the hydro-elastic effects and the effect of hull girder flexibility are capable of

significantly amplifying the hull girder stresses and thus contribute to fatigue damage as well

as to the extreme hull girder loading in container ships. The hull girder vibrations due to hydroelastic

effects is capable of doubling the stress response amidships in some cases – also in the

extreme loading cases. However, due to hydro-elastic effects whipping motion loads were

generated. Whipping is the vibration of hull girders that occurs when the bow breaks free of

the water and then re-enters. The whipping motion increased the stress on the girders. As a

result, hull fracture originated from the bottom shell plates in MOL Comfort’s midship section.

Conclusion

The MOL Comfort incident is one of the most important cases in Naval Architecture. The MOL

Comfort and her sister vessels were simply under engineered by naval architects that didn’t fully

account for enormous additional loads which were being placed on the ship. This incident helped IACS

to implement additional rules for container ships over 8,000 TEU. The final report issued by Japan

about the MOL Comfort break up concludes that the sea loads experienced by the vessel at the time of the casualty exceeded hull girder ultimate strength. [3] Since the MOL Comfort sinking, all of the sister

vessels to the MOL Comfort have been retrofitted with additional structural steel, but certainly other

ships in that size range have not. Considering the step changes being made in container ship design,

logic would dictate that additional study and consideration be taken when designing and operating such

vessels, including the installation of strain gauges to properly measure what is happening inside the

ship.

References

[1] RINA

[2] Wikipedia – MOL Comfort

[3] The Maritime Executive - IACS Acts on MOL Comfort Report

[4] Mike Povello - Update – Important Clues to MOL Comfort’s Demise

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