16 February 2024 (Lloyd's List) - NEW research on container stack collapses has found that continuing to sail through progressively worsening weather is a likely to be a contributing factor in weakening lashings to the point of failure.

An assessment of cases in which P&I insurer Gard was involved between 2016-2021, when correlated to weather data, showed that in the seven days leading up to a stack collapse, vessels had experienced deteriorating weather and increasing wave heights.

"The average wave height peaks on day seven at 6.5 m, which corresponds to gale-force winds," Gard said.

"The duration for which the vessels were exposed to sea conditions with wave heights of 4 m and above, corresponding to near gale-force winds or stronger, was 72 hours.

It was evident that the vessels experienced average wave heights that progressively increased by two and a half times during the seven-day period, Gard said.

While vessels involved in incidents spent just 5% of their time in wave heights exceeding 7 m during the incident year, half of all incidents occurred during such conditions, it added.

"Analysing the maximum wave heights experienced by vessels on the day of the incident reveals a similar pattern," Gard said.

"Essentially, despite spending 95% of their time in calmer waters, the relatively small percentage of time spent in adverse conditions significantly amplifies the risk of incidents, potentially by up to 20 times higher."

Among the vessels that had a stack collapse incident, the share of vessels exposed to such high waves increased by almost 12 times from day one to day seven.

"This suggests that these vessels may not have been able to avoid such heavy weather in spite of the advanced weather routing tools available," Gard said.

This in turn, was reflected in the type of vessels on which stack collapses had been recorded. Gard analysis showed that only 3.4% of the fleet is exposed to these sorts of conditions at any point in time, but the class of vessel most exposed is 8,000 teu-12,000 teu ships.

"Weather needs to be seen in context with ship's design and size, of course, although we do see that container stack collapses happen across different size segments," Gard said.

"Despite a higher number of incidents on smaller vessels, there is a clear correlation between incident frequency, or likelihood, and vessel size. The six-year average claims frequency for stack collapses on feeder vessels is 1%, whereas for vessels over 15,000 teu, it rises to 9%."

Gard said that exposure to progressively worsening weather posed a clear risk, and the study highlighted two crucial aspects in this regard.

"The first involves the duration of exposure, while the second concerns weather thresholds, such as maximum wave height for a vessel, influenced by factors like stability, stack height and physical condition of the securing equipment. Based on our study findings there are key questions to be considered by the many stakeholders working in the liner industry."

It warned that conflicting priorities between a vessel's master and its commercial operator could see vessels pushed beyond their limits as operators put time and fuel savings ahead of safer weather routing.

It also said the length of exposure to bad weather could be contributing to the deterioration of lashing efficacy, leading to failure.

"The constant motion of a vessel in heavy seas can exert loads on container stacks, leading to the potential loosening of lashings," Gard said.

"The loosening process can start early in heavy weather conditions, especially if the ship is navigating through rough seas for an extended period."

This was particularly the case where a vessel's securing equipment was in need of repair.

"Experience shows that condition of lashing and securing equipment degrades over time because of usage and inadequate maintenance," Gard said.

"Despite these issues, containers continue to be loaded in affected slots, and repairs are postponed until drydock for commercial reasons. Our recommendation is of course that affected slots be taken out of service until repairs are carried out, but from a pure routing perspective, weather thresholds might need to be adjusted for such vessels."