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Rogue waves and shipping

One in 10,000 waves is a rogue wave. They’re increasing in size and contributing to accidents on the high seas. What can be done?

It’s still the most shocking shipping image of the past few months – the battered magenta-coloured ONE Apus limping into the Japanese port of Kobe in December, having lost up to $200m worth of containers.

There’s been at least three other cases of box spills in the Pacific in the ensuing month and a half since the Ocean Network Express vessel hit a severe storm. Why containers are falling off ships in such volumes is covered in the editor’s comment this issue. What’s clear, regardless of lashing and stowage issues, is shipping has to prepare itself for greater incidents of storms in the middle of the world’s oceans and specifically the threat of rogue waves.

The height of the rogue waves is increasing by 1% year-on-year

The 2020 loss prevention report from the Swedish Club, a P&I club, notes that heavy weather is cited in half of all claims and contributed to 80% of the financial losses for the year.

Take a look at the weather the ONE Apus encountered on the evening of November 30 – a terrifying meteorological bomb – a low of 959, essentially a category three hurricane with significantly more sea room to develop swell structure.

Weather experts tracking ONE Apus’s path suggest the storm cell it hit could have seen the ship hit by waves as high as 16 m, that is approximately the height of a five-storey residential building.

Likewise, look at the vessel track of the Maersk Essen, another high profile box spill incident. The ship lost up to 750 boxes 11 days ago on a transpacific sailing. The vessel track shows clearly how the winds switch 180 degrees and shortly after the 13,100 teu ship has a major change of course.

The accident investigations of all of these box spills will be required reading for the liner trades. It remains too early to say for sure just how big a part stormy weather had in these incidents. Regardless, deteriorating weather patterns is something shipping needs to plan for in the long term.

Warmer oceans, bigger waves

Global warming is creating more freak waves, more ferocious and sudden storms far out to sea. Ship designs – and cargo configuration – of the future will need to absorb these fast changing weather patterns.

It’s interesting to note the Irish Navy, looking at fleet replacement at the moment, are tweaking the design of their future ships because they believe climate change has contributed to far rougher weather and far bigger waves in the Atlantic.

Defined as a wave that’s more than twice as high as the background ocean, rogue waves can reach more than 30 m.

It’s estimated that one in 10,000 waves is a rogue wave – but while they’ve been the subject of marine folklore for centuries, they were first officially recorded in the 1990s. The first rogue wave measured by instruments was on the Draupner oil rig in the North Sea on January 1, 1995. Since then scientists have been trying to study them.

A 2019 study looking at two decades of wave data carried out by the UK’s National Oceanography Centre and the University of Southampton found that the height of the rogue waves was increasing by 1% year-on-year.

The researchers also found that rogue waves varied over the seasons, becoming “more rogue” in winter – that is in terms of the relative height of a rogue wave to the background waves.

Another study published last year by the the University of Melbourne, CSIRO Oceans and Atmosphere in Hobart, and the IHE-Delft Institute for Water Education in the Netherlands simulated Earth’s changing climate under different wind conditions, recreating thousands of simulated storms to evaluate the magnitude and frequency of extreme events.

The scientists claim that if we do not curb global emissions, there will be an increase of up to 10% in the frequency and magnitude of extreme waves in extensive ocean regions.

Bjorn Age Hjollo, senior project manager at e-navigation service provider NAVTOR, cites a report by the Intergovernmental Panel on Climate Change (IPCC) that the climate indices NAO (North Atlantic Oscillation) and WEPA (Western Europe Pressure Anomaly) primarily drive the increase in winter-mean wave height and periodicity, respectively, while both WEPA and NAO explain the increase in interannual variability, resulting in more frequent high-energy winters over the last seven decades. Extreme winter-mean wave heights become more frequent as WEPA and NAO positivity and variability increase.

“The most valuable information for vessels to avoid rogue waves, is to have them forecasted. However, rogue waves are most difficult to forecast, but you may use probabilistic forecasts – also known as ensemble forecasts – to identify the risk of rogue waves,” Hjollo says, adding: “A good weather and routing service may avoid many accidents, but probably not all.”

Digital solutions

Maritime and meteorological professionals all believe digital technology offers the best solution to minimise the risks brought by rogue waves.

“I believe that many of us mariners are feeling that there is rougher weather and more severe storms now than before. And yes, we are all aware of the climate change and what we read in the news and so forth. But this it is not so easy to measure for us onboard,” says Jorgen Grindevoll, an LNG carrier captain trading worldwide, who has been working at sea since 2003.

Grindevoll believes the best way is to use the tools available to avoid such weather, and that is to apply voyage optimisation and weather routing systems in daily routines onboard.

Grindevoll would like something that could visualise the statistical data and weather measurements compiled by scientists and oceanographers worldwide. This weather/climate data presented visually in a user friendly and easy accessible platform to top executives, ship designers and policy makers could make it a decision making tool for strategic business planning, Grindevoll suggests.

Hildur Smaradottir, chief commercial officer of Miros, a technology company that specialises in measuring the ocean surface, has found that global trends in wind speed and wave height are on the up, with increasingly extreme conditions predicted worldwide.

“In the past year, we’ve certainly seen some incredibly forceful weather, with Miros sensors encountering category four hurricanes in the Gulf of Mexico and super typhoons in Japan,” Smaradottir says.

According to Miros, the study of rogue waves is still a matter of active research, and several different mechanisms for their generation have been suggested. One hypothesis proposes that rogue waves are not freaks at all, but instead make up part of the normal wave generation process. Many scientists, however, are unconvinced by this conclusion.

“Accurate prediction of rogue waves could be key to minimising the risk they pose to ship and offshore operators. Though continued research lends insight into the potential processes that create rogue waves, the jury is essentially still out, and accurate prediction of such events is yet to be grasped,” Smaradottir says.

Mike Eilts, senior vice president of weather at meteorological forecasting specialist DTN, says the move towards digitalisation in shipping is making it possible to integrate more comprehensive weather data within a ship’s existing systems.Weather optimised routing is the best tool today to help ships minimise such risks, Eilts says. He expects vessel motion forecasting technology to be up next development-wise in order to help minimise navigation risks.

“Currently, wind strength and wave heights are the metrics for safe seakeeping, but analysing the wave spectra such as wave height, wave length, frequency, timing and direction is critical for smart decisions,” Eilts explains.

Vessel motion forecasting uses wave spectra with a ship’s design parameters to predict the ship’s motions and the impact of the entire sea state on the vessel.

For example, parametric rolling, which is a main reason for container loss, can be accounted for when modelling motions using wave spectra are factored into the design of the ship and cargo placement.

Ship design changes

Studies by class society DNV GL find that rogue waves may have a significant impact on loads and responses of ships and offshore structures and, consequently, their design.

According to DNV GL, although rogue waves are currently not explicitly included in classification society rules and offshore standards, due to the lack of a consensus about the probability of their occurrence, they are needed in rules calibration when formal safety assessment methodology is applied. For some less typical designs, classification society rules require or recommend some type of dynamic load analysis that makes use of wave data and wave models.

Michael Johnson, lead specialist of hydrodynamics at Lloyd’s Register, reckons despite weather services becoming ever more tech savvy, the sea remains a challenging and somewhat unpredictable environment and incidents do happen occasionally due to a combination of factors of which the sea state is one.

“The effect of climate change is a different issue; there is evidence that the oceans are becoming rougher on average because the frequency of storms has increased, but not necessarily the extremes. This is being reflected in commercial ship design, the old wave tables based on historical eyeball wave observations can now be replaced by tables based on computational models of ocean waves. Their accuracy, resolution and availability has improved hugely in recent years,” Johnson says.

Johnson says the question of rogue waves remains controversial and the design community needs to keep a close watch on related academic work, but it seems more that the unexpectedness of events during service leads to problems, rather than a deficiency in ship design.

“We can see technology having the effect of increasing safety further as the wave models become ever better and the scope of the unexpected is reduced. This should inspire improved assistance to masters and wider take up through, for example commercial routing services, or the operational guidance tailored to individual ships,” Johnson concludes.

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