Clay Maitland

On a quest for quality in shipping

Strength of Materials

Posted on | March 9, 2015 | 1 Comment

One of the reasons that wooden ships eventually gave way to iron and steel was the fact that the size of a wooden ship is limited by the strength of the component parts. This was perfectly illustrated in WWI when the shortage of merchant ships caused b  the depredations of German U-boats caused the desperate construction of wooden freighters in the US and Australia. Several of these craft, despite reinforcement of the original design, were basically “too big for wood” and were condemned.

For a century, steel has been the preferred shipbuilding medium, designs being extrapolated to construct bigger and bigger hulls. Just occasionally has design been dangerously compromised, as the tendency has been to prudently “over-engineer” in any areas where stresses might have been anticipated. We might think about the problems of brittle fracture which emerged with the all-welded Liberty ships or the way in which injudicious loading has been responsible for ships breaking in half.

The loss of the MOL Comfort, it is probably fair to say, sent a shock wave through the maritime industry, containerships having been largely trouble free during their forty year life. Despite being probably the hardest worked and most productive ships the world had ever seen, several generations of containerships had lived out their lives without any problems.

So it is interesting to see Japan’s Committee on Large Container Ship Safety has concluded in its final report that the break-up of the 8000teu ship “possibly” occurred, because the sea loads exceeded the ultimate strength at the time of the casualty. It is perhaps less than conclusive than might be wished, not least because the two parts of the ill-fated ship remain in the deep waters of the Indian Ocean. However the International Association of Classification Societies has beefed up its longitudinal strength standards for containerships, following work done on whipping and buckling of stiffened panels. All societies moreover remain responsible for all strength aspects of hull structures and there seems some confidence that the latest ships will have adequate strength.

Have we learned all we need to know, bearing in mind the growing list of ships that are more than twice the size of the MOL Comfort? We still have owners looking for lighter ships and interest in building bigger than 400m in length. Maybe there is a little more caution in ship design with these extreme sizes. Nobody wants to see the steel ship going the same way as the wooden ones if the strength of materials proves inadequate.

 

One of the reasons that wooden ships eventually gave way to iron and steel was the fact that the size of a wooden ship is limited by the strength of the component parts. This was perfectly illustrated in WWI when the shortage of merchant ships caused b the depredations of German U-boats caused the desperate construction of wooden freighters in the US and Australia. Several of these craft, despite reinforcement of the original design, were basically “too big for wood” and were condemned.

For a century, steel has been the preferred shipbuilding medium, designs being extrapolated to construct bigger and bigger hulls. Just occasionally has design been dangerously compromised, as the tendency has been to prudently “over-engineer” in any areas where stresses might have been anticipated. We might think about the problems of brittle fracture which emerged with the all-welded Liberty ships or the way in which injudicious loading has been responsible for ships breaking in half.

The loss of the MOL Comfort, it is probably fair to say, sent a shock wave through the maritime industry, containerships having been largely trouble free during their forty year life. Despite being probably the hardest worked and most productive ships the world had ever seen, several generations of containerships had lived out their lives without any problems.

So it is interesting to see Japan’s Committee on Large Container Ship Safety has concluded in its final report that the break-up of the 8000teu ship “possibly” occurred, because the sea loads exceeded the ultimate strength at the time of the casualty. It is perhaps less than conclusive than might be wished, not least because the two parts of the ill-fated ship remain in the deep waters of the Indian Ocean. However the International Association of Classification Societies has beefed up its longitudinal strength standards for containerships, following work done on whipping and buckling of stiffened panels. All societies moreover remain responsible for all strength aspects of hull structures and there seems some confidence that the latest ships will have adequate strength.

Have we learned all we need to know, bearing in mind the growing list of ships that are more than twice the size of the MOL Comfort? We still have owners looking for lighter ships and interest in building bigger than 400m in length. Maybe there is a little more caution in ship design with these extreme sizes. Nobody wants to see the steel ship going the same way as the wooden ones if the strength of materials proves inadequate.

 

Comments

One Response to “Strength of Materials”

  1. Chris Allport
    March 10th, 2015 @ 10:58 am

    Let’s hope that those Owners looking for bigger and lighter vessels take note of this article!

    In addition to the MOL Comfort, over the 40 years you refer to there have been at least two other significant incidents where container vessels broke their backs, MSC Carla and MSC Napoli. These three incidents should serve as a further warning to Owners not to force Class and Shibuilders to push the limits too far.

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