It is a bold statement – that the Oceanbird concept could reduce ninety per cent of the emissions compared to a conventional vessel. What led to this conclusion? KTH professor Jakob Kuttenkeuler discusses the project, which he started working on twenty years ago.
When the young aerospace professor Kuttenkeuler competed in sailing races, he created a simulation program to optimise his performance. Twenty years later, that program is the basis for the calculations showing that the Oceanbird concept could reduce emissions by ninety per cent.
Wallenius has added pieces to the program, as well as SSPA, which mainly contributes with the hydrodynamic forces from hull, propeller, rudder, fins, and the aerodynamic forces from the wings. The Oceanbird team wants to know what happens with for example the emissions if the wings where bigger/smaller, if the speed increases/decreases, with less/more ballast water and so on. Kuttenkeuler, nowadays a professor at KTH Centre of Naval Architecture, has puts these parameters in the program.
Using historic weather conditions
He selects the departure and arrival destinations, normally Southampton-New York, but also across the Pacific, and adds historic weather conditions. The computer program then optimises the sailing route according to the authentic weather conditions. The virtual vessel sets off on a round-trip twice a month for a decade, thus crossing the sea 480 times. After that, there is a lot of data to transform into statistics.
‘The devil is in the details and during this last year, the simulations got much more detailed. We have been looking at for example varying reefing schemes. The telescopic function is useful in many ways,’ says Kuttenkeuler.
Also read: Wallenius and Alfa Laval in joint venture to realise wind-powered Oceanbird
Data meets a captain’s experience
The program chooses the optimal route to get to the destination using the wind as effectively as possible. This will also be a vital component in real life, the optimal routing is actually as vital as any other component of the fine-tuned ship system.
‘There is a danger in trusting the computer simulations too much. The computer loves hard weather to sail fast, whereas the captain onboard might not be equally enthusiastic about going through passages with winds up to twenty metres per second and waves reaching seven metres. That’s why it’s so great that we have one of Wallenius’ captains in the project. He contributes with so much experience that is valuable for making this work in real life.’
Three equations
The foundation of the simulations are basically three equations of equilibrium working in harmony. One is related to the thrust: the forces that make the vessel go forward (the wings and sometimes engine) need to be equal to the forces slowing it down (the sum of the resistance components, mainly from the hull). Second is sideways equation. The vessel will not go straight forward like a conventional cargo vessel, but slightly on the side like any other sailing boat (this is often referred to as leeway). Third equation is coming from the wind, pushing the wings high above water, the heeling equation.
‘That was one thing that surprised me,’ says Kuttenkeuler. ‘Before we did the simulations, I thought the vessel, being the world’s highest sailing vessel, would heel a lot more and I was worried about the cargo and the amount of ballast water needed to maintain stability. But the specially designed hull stabilises the vessel, so it won’t tilt more than maximum five degrees even without ballast. With ballast you won´t notice it onboard.’
SSPA maps uncertainties
To verify the calculations, both KTH and SSPA have conducted extensive model testing in water tanks and open water. SSPA are also working on a scientific report to map uncertainties in the entire simulation chain. When the report is published in the end of 2021, it will be public and available for anyone to read.
‘The transparency is one of the things that are so great about this project. Scientists and students in the project have already published a lot of interesting reports, and more will come,’ says Sofia Werner, Manager Strategic Research Hydrodynamics at SSPA.
Oceanbird
Wallenius, KTH and SSPA have been partners during the development project, which is supported by the Swedish Transport Administration. The development project, called wPCC, started in 2019 and ends during 2022. In September 2020, the collaboration presented the Oceanbird concept.
The Oceanbird car carrier concept started as a vision to achieve emission-free shipping. In July, this year, a fifty-fifty joint venture between Wallenius and Alfa Laval was made to make the vessel a reality. AlfaWall Oceanbird will focus on the development and realisation of technology for fully wind-powered vessel propulsion. Plans are that the vessel sets sail in late 2024.
Also read: Wind powered car carrier to set sail in late 2024
