Green Shipping January 2021
A giant sail for a ship
Could a unique car carrier, with a hull designed to harness wind power, be the future of deep-sea transportation?
Several existing wind-powered technologies are installed during retrofi ts, but one ongoing Norwegian project envisions a hull purpose-built to harness this renewable energy source
Vindskip is a 199m-long, 6,600-capacity wind and LNG-powered car carrier design by Lade AS, which aims to off er the industry’s lowest emissions in the deep-sea car carrier market. To achieve this, the company has developed Vindskip’s three-part dynamic system; its patented Wind Propulsion System, a Cruise and Propulsion Power system and fi nally, its Weather Routing Module
Terje Lade, designer of Vindskip, tells Th e Naval Architect that he originally found inspiration for the project when designing for an entirely different sector: “While working with speed sailing boats, a sort of ‘greed for speed’ turned into a concern for the environment, and I started thinking ‘how can I use this knowledge to design a ship that doesn’t run on HFO, and that was the basis of Vindskip.”
How does it work?
Vindskip has been compared to a giant sail as its hull is shaped like an ‘airfoil’; the cross-sectional shape of a wing, blade or sail that, due to airfl ow along its form, generates pull and drag when travelling through air or fl uid. In Vindskip’s Wind Propulsion System, different levels of pressure are created as Apparent Wind, the wind measured onboard a ship in motion, fl ows over its hull, generating a positive pull in the vessel’s direction as a function of the Apparent Wind Angle of Attack.
Th e Angle of Attack is defi ned as the angle between the ship’s chord line (the central line running longitudinally along the hull) and the Apparent Wind, and Vindskip can achieve some level of pull (negative force coefficient) between the Angle of Attack values of 18-180 degrees (see Figure 1). Th is allows it to operate well in conditions seen during deep-sea voyages, as Lade explains: “Th ere are some small optimums along the yaw angle (Angle of Attack) line, and the best is about 80-85 degrees, but it operates very well from 40 up to 90 degrees, and that is actually the range you are operating within when you are out on the sea.”
Sails are traditionally asymmetrical airfoils, but Vindskip’s hull is a symmetrical airfoil, allowing it to harness Apparent Wind from both starboard and portside. Lade stresses that the vessel’s ability to function between 18-180 from either side of the ship is what separates it from its sail-based predecessors: “It has to function under all conditions, because if you are carrying valuable goods then you have to have a high regularity. It cannot operate as a sail ship, as you would have to chase the wind and the regularity would be very poor.”
Below 18 degrees Angle of Attack Vindskip does not generate pull but its drag is marginal, Lade points out, adding that even at zero angle of attack (also known as headwind) the ship will still experience very low drag, giving it the upper hand over regular car carriers and even the cargo it may carry. “In fact, it’s so low it’s about a 0.15 drag coeffi cient, if you compare this with a car, like Tesla for instance, which has the lowest drag coeffi cient in the current market of 0.24. While for an ordinary ship this is much higher, around 0.6, and the curve displayed on Vindskip’s graph (Figure 1) doesn’t even go that high,” he comments.
A well-balanced ship
One of Vindskip’s major advantages over standard car carriers is a projected 75% drag reduction and, in turn, an estimated 60% reduction in fuel. While there’s no doubt that the drag abatement accomplished by Vindskip’s Wind Propulsion System contributes to these figures, Lade also highlights the importance of the ship’s hydrostatic underwater hull design:
“Th e underwater hulls of ordinary ships have flat bottoms. That means they are moving along their route like a snake on the water, and they have to use the rudder to align for this movement. By doing so, they are breaking and slowing down the ship – it’s like driving your car with the handbrake on and that will cost you a lot of fuel. Whereas Vindskip can operate in the Atlantic with a rudder angle of 0-2%.”
Lade says this narrow rudder range is possible because of the ship’s balance due to its underwater hull; it’s designed with a trimmer that provides stability in place of a traditional heavy keel used for counterbalance on sailboats. As a result, Vindskip requires only 400tonnes of ballast water to transport its 6,600 RT43 cars, in contrast to the 5,000tonnes required by a standard 6,000capacity car carrier. “This gives it a great advantage with respect to the resistance through the sea, which is refl ected with regard to the fuel consumption with its much lower displacement than a reference ship,” he adds.
Maintaining consistent speed
Wind conditions in the Atlantic, where Vindskip aims to travel, will vary over time, Feature 1 | WIND Could a unique car carrier, with a hull designed to harness wind power, be the future of deep-sea transportation? A giant sail for a ship Inspired by airfoil techniques harnessed by the aviation and sailboat industries, Vindskip’s wind-powered propulsion enables a 63% reduction in CO2 Green Shipping January 2021 3 Feature 1 thus if the ship operated on wind-powered propulsion alone it would be unable to sustain the 14knot service speed required to complete nine transatlantic trips annually, a number stipulated by Vindskip’s client, an unnamed European car manufacturer.
An LNG-powered propulsion system provides the secondary power necessary for the vessel to maintain constant speed throughout a voyage, automatically adjusted with cruise control. Devised by Brunvoll Volda, Stadt and Høglund Marine, the system is capable of running on three diff erent modes that cover a range of power outputs (see Table 1) and allows for the mixing of LNG and Liquifi ed Biogas (LBG), Liquefi ed Bio Methane (LBM) or Liquefi ed Synthetic Methane (LSM). This enables Vindskip freedom to bunker according to fuel availability and, according to the company, sets out a pathway for the ship to potentially reach close to zero emissions with the introduction of LBM or LSM in the future. But the all-important question remains, how much CO2 can Vindskip currently save while travelling in Atlantic waters?
In 2019, Vindskip’s Weather Routing Module (WRM) was used alongside historical weather to simulate a year’s worth of voyages. Designed by the German research institute Fraunhofer Center for Maritime Logistics and Services, Vindskip’s WRM will be utilised onboard the vessel when in-service to calculate its optimum route. It takes into account the ship’s aerodynamic, hydrodynamic, fuel consumption, hull and rudder characteristics as well as weather forecast data
Along the WRM’s optimised route lies a series of checkpoints, known as waypoints, which monitor the ship’s progress throughout the voyage via a digital Speed Pilot and Track Pilot, as Lade explains: “Th e Track Pilot knows the route and when Vindskip is entering a waypoint the pilot will know what course it’s on and adjust accordingly, the Speed Pilot knows the time it should be at the waypoint and will adjust the speed to reach the next waypoint in the right time.”
Speed is then altered by changing the propeller pitch and revolution, followed by starting up an engine if more power is needed: “Th is is all done automatically, and this means that Vindskip can follow a route autonomously. You don’t need people on the bridge, other than when entering or exiting a harbour,” Lade adds.
Autonomously, in this case, falls into level one of the International Maritime Organization’s degrees of autonomy, whereby a vessel has automated processes and decision support, but seafarers are onboard to operate and control shipboard systems and functions. “Onboard (Vindskip) there will be an ordinary number of crew due to the value of the cargo. It’s so high that nobody would accept that the ship was sailing without them,” Lade comments.
Results and regularity
Nine transatlantic round trips, between Emden – Jacksonville – Vera Cruz – Emden – were simulated by the WRM and it was found that, compared to a reference 6,600capacity car carrier, black carbon and SOx (0.5% m/m sulphur) were reduced by 100%, NOx reduction by 96% and CO2 by 63%. But Lade comments that these calculations were made using wind and LNG-powered propulsion, which he says provides scope for further reductions in the future: “Th e Vindskip propulsion system is designed in a way that you can mix LNG with biogas, and although our calculations are based on LNG and wind, if you mix in biogas you will, of course, improve the situation with regard to the CO2 emissions.”
Any wind-based propulsion throws regularity into question but Lade highlights that the WRM’s simulations also found marginal differences in voyage duration and fuel consumption: “During these nine voyages, the duration for one round trip varied by three hours. Th e maximum voyage duration in hours was 771, and the lowest was 768.”
“Th ere was an average fuel consumption of 15.1tonne of LNG. And the average fuel consumption from trip-to-trip varied with 1.5tonnes a day, and I think this is all quite amazing considering the weather, waves and wind in the Atlantic.”
The next step
Vindskip has continued to gain ground since the project’s launch in 2010 and the company hopes to sign a newbuilding contract at the end of 2021 and has begun discussions with four Chinese shipbuilders that remain anonymous. With that, Vindskip could hit the waves not too far in the distant future: “To build a ship like Vindskip it takes around 30 months, so if you say nearly three years of construction time and if we start building at the beginning of 2022, we’re looking at (completion) by 2025,” Lade concludes. NA