The rise of the wind ships

Could a new generation of innovative propulsion technologies that harness the power of the wind help the shipping industry clean up its act? Jon Excell reports

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Econonwind's ventifoil system installed on the deck of the DFDS cargo vessel Lysbris Seaways

Commercial shipping - for many years resistant to the low carbon revolution sweeping other areas of transportation - is changing fast.

Faced with a combination of rising fuel prices and an industry-wide strategy to cut greenhouse gas emissions by at least 50 per cent over the next 30 years, the sector  (thought to be responsible for around 2.5 per cent of global GHG emissions) is innovating as never before in an effort to boost fuel efficiency and reduce its environmental impact.

From the development of novel hybrid electric propulsion systems to AI driven improvements in operational efficiency, no stone is being left unturned in the quest to slash emissions. But arguably some of the most intriguing advances are being made in a field that harks back to the earliest days of seafaring: wind propulsion.

We don’t see how we can make the speed and depth of the change without wind propulsion taking a significant load

Gavin Allwright - International Windships Association (IWSA)

Whilst no-one’s quite proposing a return to the great age of sail - where world trade was utterly reliant on the power of the wind - many believe that a new generation of wind propulsion systems - an eclectic mix of innovative sails, strange deck mounted wings, kites and weird hull designs - could play a key role in the sector’s future.

Gavin Allwright, who heads up the trade body representing companies in this field - the International Windships Association (IWSA) - has witnessed this growing interest first-hand. The association has grown from 12 to just over 100 members and partners since 2014: a clear reflection, says Allwright, of the growing seriousness with which wind propulsion is being treated. “We don’t see how we can make the speed and depth of the change without wind propulsion taking a significant load,” he told The Engineer.

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Many of the technologies at the heart of this burgeoning field have actually been around for some time. Flettner rotors, for instance (discussed later in this article) were invented over a century ago. What’s changed, said Allwright, is that there are now tangible examples of these systems in action and, in many cases, verified figures to back up the developers’ claims.

At the most recognisable end of the wind-assist spectrum are innovations in soft sail systems. The increasing sophistication of automation and route optimisation systems have revived interest in seafaring’s original power source, and there are now a growing number of examples of larger vessels using smart soft sails alongside auxiliary propulsion systems. In one notable development, French naval architect VPLP recently unveiled a design for a 121 metre long roll-on/roll-off (RORO) vessel that will be used to transport components of the Ariane 6 rocket from Europe to Guiana. The ship’s main propulsion system (a dual fuel LNG MDO engine) will be assisted by four Oceanwings; fully automated wing-sails which are each supported by a 30m high mast and measuring  a total of 363 square meters.

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VPLP's design for a RORO vessel that will be used to transport components of the Ariane 6 uses four fully automated Oceanwings

There is also growing interest in the use of rigid hard sails, which are sometimes preferred over soft sails because of the potential for incorporating different aerodynamic structures or even photovoltaic coatings.

As with soft sail innovations, there are numerous ongoing initiatives in this area exploring the application of the technology to vessels of various different sizes. In one recent development, Japanese firms Mitsui OSK lines and Oshima shipbuilding received Approval In Principle from marine classification body ClassNK to build a 100,000 DWT bulk carrier equipped with a telescopic hard sail system that the group claims could reduce fuel usage by as much as 8 per cent.

Whilst the ability to automate, deploy new materials, and use data to optimise performance is breathing fresh life into the use of traditional sails, they do come with some significant challenges as they are scaled up in size. Not only do they take up large amounts of deck space (valuable real-estate in the commercial shipping sector) but they can also induce a significant amount of heeling (or tipping from side to side) in the vessel.

One concept that potentially gets around this problem is an innovative device known as a suction wing, a deck mounted vertical foil claimed to provide considerably more power per square metre than a normal sail at a fraction of the height.

Based on technology originally pioneered by marine explorer and conservationist Jacques Cousteau, these systems use a powered suction device mounted within the wing to suck in the boundary layer around the foil and increase its propulsive efficiency.

One of the key players here is Netherlands firm Econowind, whose so-called Ventifoil technology – a non-rotating wing with vents and a powered internal fan - can either be retrofitted to the deck of a vessel, or deployed within containers that are added and removed  as and when required.

Econowind's technology can be deployed in containers that are added to and removed from the deck as and when required

The company’s CEO Frank Nieuwenhuis explained that during operation and when the wind conditions are favourable, the system increases the speed of a vessel enabling the captain to throttle back the propulsion system without reducing the voyage time.

Late last year (2019) the firm installed a prototype system, consisting of two 10 metre foils that automatically fold out of a 12 metre container, on the deck of DFDS Cargo vessel, Lysbris Seaways. According to Paul Woodall, director, Environment & Sustainability at DFDS, although a mechanical fault has brought this trial to a premature end, preliminary results show that a positive effect was achieved.

At the time of writing, Econowind was also poised to install a larger permanent system aboard MV Ankie, a 3,600 DWT cargo vessel operated by Van Dam Shipping. Commenting on the potential fuel savings resulting from this application  Niewnhuis said: “we expect that on a really good day we will save 20 per cent and over the year we would expect the unit to do between 8 – 10 per cent.”

Whilst Econowind’s unit takes up a fraction of the deck space occupied by conventional sails, other innovators are looking beyond the deck, and eyeing up the use of giant kites to tap into the potential of the considerably greater wind resource in the skies above a vessel.

One of the most exciting technologies in this area is Seawing, an autonomous system developed by French company Airseas. The firm was spun out of Airbus in 2016 with the express purpose of finding marine applications for modelling and flight control expertise gained in the aerospace sector.

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Concept image of Airseas' Seawing technology in action

The technology consists of a giant kite that is deployed and refurled at the push of a button, and which, the company claims, can deliver average fuel savings of 20 per cent.

Luc Reinhard, who heads up the firm’s business development activities, explained that whilst other kite-based systems have been trialed, Seawing’s autonomous operation, and the software tools and flight control systems that underpin its operation set it apart from other technologies. “What is really innovative about our solution is this notion of automation software, digitalisation of the product so it’s really simple to use by the crew members onboard ships”

The key components of the system are a mast that allows the wing to be deployed, a winch to roll the 500m long cable, storage for the wing when it’s not being operated, and the wing itself.

During operation the wing flies at an altitude of around 150m metres at a 30 degree angle from the ship.  A flight control pod positioned directly beneath the wing dynamically adjusts the flight path, moving it through a series of positions and repeatedly dragging it out of what Reinhard describes as “its comfort zone”. It’s the wing’s efforts to return to this position that generate most of the device’s traction.

The company has already conducted a number of ground tests and sea trials using scaled down versions of the technology, and is now poised to begin its first commercial installation, which will see a 500 square metre wing installed on an Airbus RORO vessel used to transport aircraft parts. The firm also recently signed a contract with Japanese Ship owner Kawasaki Kisen Kaisha Ltd (aka K Line) to install an even larger 1000 m2 wing on one its vessels, with an option to install upto 50 further systems if this application is successful.

Ship design changes slowly – which is why many of these technologies currently being deployed are retrofittable solutions.

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The Vindskip concept turns the ship's hull itself into a giant wing

However, Vindskip, a radical concept developed by Norwegian engineer Serje Lade, offers a glimpse of how future vessels might be designed from the ground up to tap into the wind resource. Lade’s aerospace inspired design turns the hull of the boat itself into a wing, a symmetrical airfoil that generates lift that can be used to generate pull.

Lade told The Engineer that the hull works in tandem with the propulsion system and meteorological data to keep the ship at a constant speed. He has also been working with engineers from the Fraunhofer Center for Maritime Logistics and Services on the development of algorithms to calculate the optimum wind angle for the design of the vessel.

Tank testing and wind tunnel tests of scale models and CFD simulations indicate that the design could enable fuel and emissions savings of as much as 60 and 80 per cent respectively, he said.

Whilst concepts like Vindskip are probably many years away from commercialisation, other technologies are already having an impact. And the most widely deployed of the emerging systems is the Flettner rotor, an intriguing concept originally developed almost a century ago, which is now under serious consideration by some of the shipping industry’s biggest players.

Similar in appearance to suction wings, Flettners operate on a very different principle, exploiting a curious aerodynamic phenomenon known as the magnus effect, the same force that causes a spinning tennis ball to swerve.

Looking rather like vertical cylinders mounted on the deck of a ship, these powered devices rotate around their own axis. This rotational speed can be adjusted depending on the wind speed and direction, and the interaction between the surface of the rotor and the wind creates a lift force that generates additional thrust.

Whilst a number of firms are actively working on the development of the technology, the leader in terms of the number of installations is Finnish company Norsepower systems, which makes the bold claim that its Rotor Sail technology - if applied to the entire global tanker fleet  - would reduce annual CO2 emissions by more than 30 million metric tonnes.

Back in 2018, the company was behind the first ever application of the technology to a passenger vessel when a Rotor Sail technology was installed on Viking Grace, an LNG-fueled passenger ferry. Last year, it announced plans to install a 30 metre high system aboard the M/V Copenhagen, a hybrid passenger ferry operated by Scandlines.

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Flettner rotors installed on the Maersk Pelican , a 109,000 DWT tanker.

The firm also recently announced results of a year-long installation of two 30 x 5m Rotor Sails on the Maersk Pelican , a 109,000 DWT tanker.  The results of this trial were analysed by Chris Craddock, Technical Advisory & Ship Performance Manager at Llloyds Register, who told The Engineer, “We have  independently verified the performance of Norsepower’s Flettner rotor system through a 12 month in-service trial - the aggregated total fuel saved for propulsion was 8.2 per cent. This was closely in-line with the expectation of Norsepower.”

Craddock added that the lessons learnt from this project have been incorporated into a Flettner rotor savings calculator which can be freely used to estimate the fuel savings for many types of ship types sailing on any trading route across the globe

Having demonstratable figures like this has, said Allwright, created real momentum in the sector. “Two or three years ago we had very few demonstration vessels out there and there weren’t enough reference points for the industry to say ‘right now we understand’ and get an understanding of what the savings might be.”

Lloyds Register’s Craddock, though broadly positive about the role that could be played by wind assist systems, warned that there is still a long way to go. “ Wind technologies are generally acknowledged as a credible energy saving technology that could be applied to merchant shipping and reduce carbon emissions for certain ship types and sailing routes,” he said.   “However, since wind technologies are generally at a low level of technology readiness, there is a cautious interest by most of the market, with some of the larger charterers directly investing in technology development programs and pilot projects. As more technology demonstration pilot projects are successfully completed raising confidence in the technology, and new build contracts are placed specifying these technologies, payback periods will drop and there will be a steady increase in the uptake of the technology.”

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Flettner rotors exploit the same aerodynamic phenomenon that causes a spinning tennis ball to swerve: the Magnus effect

DFDS’s Paul Woodall took a similarly balanced view. “We can leave no stone unturned in pursuit of continued efficiency improvements. This must include being available for testing any new technology, including various types of wind assistance. There is no single silver bullet that will bring shipping’s GHG emissions down to the required levels, it is a long tough road. Shipping is a multifaceted  industry  that will require a number of different solutions models.”

The technology’s current momentum will no doubt lead to a greater number of applications in the years ahead. But it’s clear that while wind-assist has an important role to play, it’s not going to single-handedly address the shipping sector’s ambitious targets.