The oceans are the main transport routes for world trade, with 90% of traded goods transported by sea. Over time, the size of containerships has increased, enabling more goods to be transported in a single vessel. As well as improving efficiency, the increased sizes of containerships have also lowered shipping costs.

Although ultra-large containerships have been designed, they have never been built to carry more than 25,000 TEU (twenty-foot equivalent unit). For comparison, the largest containerships as of today carry up to 24,000 TEU. One of the reasons the designs for ultra-large containerships carrying more than 25,000 TEU have not been put into practice is because experts have been unable to calculate the design value of wave-induced loads, and the impact they would have on these ships. Since larger and stronger waves can destroy hulls and entire ships, the lack of information in this area has hindered the ability of the shipping industry to progress.

In response to this, Professor Jeom-Kee Paik and Professor Giles Thomas from UCL Mechanical Engineering undertook a research project to find a method to accurately calculate the design values of wave-induced loads. This research was funded by the Lloyd’s Register Foundation, in association with the research programme for ‘Engineering a safer world’.

Finding out about force on ship hulls

“While in service, ships are subjected to various types of extreme conditions and accidents, such as structural collapse, fires, explosions, collisions or grounding, which can lead to catastrophes affecting personnel, assets and the environment,” Professor Paik explains. “My project has developed advanced methods to effectively manage extreme conditions and accidents and ultimately resolve such challenges.”

Professor Paik and Professor Thomas designed a new methodology for determining the design values of wave-induced loads that affect ships, particularly on their hulls. Their method is based on probabilistic approaches, rather than approaches based on the past experiences of current industry practices. These probabilistic approaches were applied to the realistic scenarios a ship could face.

The team looked specifically at vertical bending moments – which happen when force is applied – on ship hulls. For the purpose of the research, they applied their new method to three types of containership. One was a 9,200 TEU containership, which was validated by a reference ship of a VLCC class tanker. The second one was a 22,000 TEU containership, and the final one was a hypothetical 25,000 TEU containership.

Preventing accidents

The team found that their new method for measuring wave-induced loads on the ships had a high level of accuracy. This information has the potential to enable ultra-large containerships carrying more than 25,000 TEU to be built. It also means that operating expenditures can be economised, since building costs and repair costs can be lowered if ships have been designed to withstand the required level of wave-induced loads.

Currently, ocean waves can and do destroy ship structures. Professor Paik explains that waves that are harsh enough to destroy ship structures can result in total loss of the ship, or cause fires before sinking. The ship’s hull can even break in two in certain waves. “The developed method can be used to resolve such issues,” he says.

The results from the project are now becoming industry practices. These practices are being embedded into advanced safety design and the engineering procedures for designing ultra-large ships. Essentially, the method developed by the team has made it possible to define the design values of the wave-induced loads acting on larger and safer ships, despite extreme ocean environmental conditions.   

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