Barriers to success21 December 2022
In January 2022, a cargo ship struck a turbine foundation at the under-construction Hollandse Kust Zuid wind farm off the coast of the Netherlands, following a collision with a tanker. Fortunately, the accident didn’t lead to any fatalities, but with the North Sea becoming an increasingly popular site for wind farms, industry insiders have started looking at ways to stop similar incidents in future. Enter MARIN, a Dutch maritime research institute that has tested several barriers aimed at preventing collisions between ships and offshore turbines. Andrea Valentino speaks to Bas Buchner, president; Yvonne Koldenhof, senior project manager and team leader; and William Otto, senior project manager; at MARIN to understand the results of their tests – and how they see anti-crash technology developing in the years ahead.
Whatever your job, Mondays are never easy. But no matter how much you’ve struggled, you’re unlikely to have had a week begin quite as badly as the crew of the Julietta D. A bulk carrier sailing in the North Sea, not far from the Dutch coastline, the ship collided with another vessel on Monday 31 January 2022 – and that was just the start of her troubles. Pretty soon, the Julietta D was floating adrift, its engine room filling with water and its 18-person crew rushing to evacuation helicopters. Nor were the ship’s travails finished even then. Drifting helplessly for several hours, the Julietta D crashed into the under-construction Hollandse Kust Zuid wind farm, hitting and damaging at least one foundation.
As farcical as this scene sounds, the story of the Julietta D actually speaks to a genuine difficulty. According to recent research, about 80 ships get loose in the North Sea each year. And given 2,500 turbines are due to be installed in the area by 2030, the chance of future collisions between towers and ships is only rising. Nor is this mere conjecture. As the Dutch government has warned, the risk of an unhappy meeting between vessel and turbine is increasing from 1.5 to 2.5 times a year, on average. It goes without saying, meanwhile, that any repeat of the Julietta D can have dire consequences for shipowners and turbine operators, forcing both parties to make costly repairs in what are already torrid conditions. And that’s before you consider the dangers to crew or passengers aboard a stricken ship.
No wonder, then, that industry insiders are working so hard to make the seas secure for both shippers and energy providers. Buoyed by careful planning and new technology, researchers are developing a number of ways to keep drifting ships safe from turbines in the sea. Yet, if these platforms are inarguably ingenious, to be genuinely successful in the field they also require close collaboration with other stakeholders. Battle through these obstacles, however, and the North Sea could soon be transformed forever – if commercial companies are forward-thinking enough, anyway.
Hitting on something
The North Sea is one of the busiest shipping regions on earth. An estimated 250,000 vessels sail through the Dutch portion of the sea each year alone, with major ports like Bremen and Antwerp also located nearby. This is a situation which could soon lead to problems – especially as offshore wind becomes more popular across the region. “Obviously the risk of a collision increases with the amount of turbines installed,” says Yvonne Koldenhof, senior project manager and team leader at Maritime Research Institute Netherlands (MARIN), “which is why collisions have not been common till very recently and why, if we do not think about mitigations, it will be common in the near future.”
As the senior project manager at MARIN implies, incidents like with the Julietta D have been mercifully rare so far. But if anything, that makes the looming threat even more worrying. We don’t know, Koldenhof emphasises, what would happen if a turbine collapsed right onto a ship post-collision – though given their blades alone can weigh as much as 55t, the answer can’t be anything good. And with the whole structure coming in at around 300–400t, Koldenhof fears that any crash would surely put the crew at risk. And if that wasn’t bad enough, the North Sea’s role as a major thoroughfare for cruise ships and ferries means that human life could be threatened in other ways too. Once again, this is currently a theoretical risk. But given ferry disasters can quickly cause dreadful casualties – the 1993 sinking of the Herald of Free Enterprise off Belgium killed 193 – Koldenhof is right to be concerned. Then there’s the potential impact to turbine operators themselves. Given a 50MW offshore farm can cost up to $2bn merely to build, you have to imagine that repairing any ship-induced damage would be eye-watering.
Of course, it’d be wrong to suggest that the shipping industry is oblivious to these dangers. If nothing else, anchors are the obvious solution here, designed as they are to slow or stop a vessel that’s run amok. But as Koldenhof says, anchors are not always enough to stop a drifting ship. That could either be because their chains break or because they can’t hold ground, or even because active intervention by the crew in poor weather may actually make the situation worse. Given the infamous reputation of the North Sea as a place of bad weather – where snow and winter winds are common – that’s hardly a trivial concern. It’s surely not incidental that the Julietta D herself first got into trouble during inclement winter weather.
Buoy oh buoy
If January’s chaos offered a warning to users of the North Sea, MARIN took the incident as an opportunity. That, at any rate, is clear from the range of options the Wageningen-based team has developed to stop ships from wreaking havoc on new wind farms. These solutions begin, says William Otto, with so-called ‘surface buoys’. “A line is equipped with small floating buoys every 50m, which prevents the ship from drifting over the line,” explains Otto, a senior project manager at MARIN. From there, he continues, larger buoys are installed every 500m or so. These are used to connect what Otto calls “mooring legs” – chains anchored to the seabed.
All this sounds fiendishly complicated. But the physics, Otto summarises, is simple enough. If a heavy-enough object, say a drifting ship, succeeds in stretching the line and dragging an anchor, nearby mooring legs can take up the slack. In this way, the vast kinetic energy of the intruder can quickly be absorbed. The vessel is stopped and nearby wind turbines are kept secure. Nor are surface buoys the only project that Otto and his team are busy perfecting. By using vast suspension nets that are 1,500m long and tensioned between two monopoles, MARIN hopes to stop errant vessels in their tracks here too. Another strategy involves underwater hooklines, whereby a ship’s anchor is looped around a wire floating five metres above the seabed.
Whatever the system, at any rate, it’s clear that MARIN hasn’t simply stuck to the theory. On the contrary, Otto explains how his team tested their theories vigorously, using scale models in a giant basin. A 176m drifting vessel, for example, was represented by a 4.4m wooden model. “At this scale we can measure realistic ship motions and line forces,” Otto adds, “as at this scale we have decades of experience for testing all kinds of mooring systems.” A fair point: MARIN’s bread-and-butter has, for decades, been testing moored ships, work that shares certain similarities with the North Sea’s current predicament. It helps, too, that tinkering with designs was straightforward due to their smaller scale. That meant, for instance, that MARIN could quickly identify the problem of nets getting trapped beneath vessels – a problem handily solved by integrating buoys, keeping the nets floating nearer the water line.
A step forward
The ultimate question, of course, is how successful MARIN’s models actually were at stopping runaway ships. The main headline here is essentially positive. As Otto laconically puts it: “The barriers were able to catch the vessel and bring it to a standstill.” Consider what MARIN’s achieved so far and this seems like a fair assessment. Though its barriers haven’t yet been tried out in the wild, they were able to halt loads weighing between 150–300t. Even so, Otto is careful not to overstate his employer’s triumphs. For one thing, the barriers weren’t tested to stop specific vessels in specific weather conditions. Given the North Sea’s volatility – either in terms of wind or waves – that’s clearly something that’ll need attention eventually. More broadly, MARIN hasn’t yet investigated how these barriers would be installed in the real world, nor how a stricken vessel might be untangled from all those nets and anchors. As Otto stresses, MARIN has to be careful “not to claim success” based on what are only tentative first steps.
All the same, speak to others at MARIN and it’s clear that industry insiders understand the potential of their work. “We have invited shipping companies, turbine operators and organisations such as the Coast Guard to the demonstration day of our open innovation project,” says Bas Buchner, MARIN’s president. “They responded positively.” The team’s work is being recognised in other ways too: the Dutch Association of Shipping Companies nominated them for a prize this year, recognition of what Buchner calls their “proactive and innovative” work on ship safety. Yet, as Buchner continues, more enthusiasm is needed if the North Sea is ever to be crisscrossed with mooring legs for real. A maritime research institute, MARIN is focused on just that: research. But actually getting barriers built commercially requires a profit-oriented firm to push development forward. To that end, Buchner is considering the creation of a ‘joint industry project’ whereby industry and government can collaborate to finally keep vessels and turbines safe at sea. Given how awful that Monday back in January 2022 almost was, that’s surely just as well.
The approximate number of ships that get loose in the North Sea each year.
The number of new wind turbines that are due to be installed in the North Sea by 2030.