The most important structural failure mode is sagging of a loaded tanker in high waves. This is also known as hull girder failure, and in some cases it can sink a ship. The North Atlantic has the world’s most severe wave climate with significant wave heights of 16 to 17 metres. As the climate changes and winds strengthen, extreme waves are likely to become larger.
Our analysis and results
As winds become more intense in a changing climate, extreme waves are likely to grow. Projecting the exact wave change is difficult, so we have considered the following increases in wave height: 0.5 metre, 1.0 metre and 2.0 metre and the effect of such increases for five different tankers. To evaluate structural integrity we follow guidelines set by the International Maritime Organisation (IMO) for formal safety assessments. We used standard industry software to make structural reliability calculations. As an example of the results, the figure below shows calculated annual probability of failure for the Suezmax tanker. The probability is plotted as a function of steel deck cross-sectional area. The figure shows probability of failure for the Suezmax tanker.
Preparing for adaptation
It is still too early to justify changes to DNV GL’s rules and offshore standards and further studies are needed to understand the implications of climate change. The shipping industry should continue to prepare for adaptation and work towards a more safe and sustainable future. For more information about this case study see the report “Adaptation in a changing climate” in the right hand column.
Our results show similar trends for all ships we analysed. When significant wave height goes up by 1 meter, reliability is maintained if the amount of steel in the deck is increased by about 5 to 7%.