Researchers at Chalmers University of Technology in Sweden have created a unique method to further develop hydrofoils that can significantly increase the range of electric vessels and reduce the fuel consumption of fossil-powered vessels by 80%. An open access article on their work is published in the Journal of Marine Science and Engineering.
Hydrofoils, like fenders, lift the hull of the boat above the surface of the water and allow the boat to travel with significantly less water resistance. In recent years, hydrofoils have revolutionized sailing, with hydrofoils flying the boats of elite sailors over the surface of the water at very high speeds. The Chalmers and SSPA researchers now want to allow the hydrofoil principle of sailing ships to also be used on larger passenger ferries, which would bring major benefits for the climate.
Longitudinal balance of forces on a NACRA 17 hydrofoil catamaran. Giovannetti et al.
The electrification of ferries cannot be done without drastically reducing their watertightness. This method will allow the development of new foil designs capable of reducing resistance by up to 80%, which would significantly increase the autonomy of a battery-powered vessel. This way we could also use electric ferries over longer distances in the future.
—lead researcher Arash Eslamdoost, co-corresponding author
Even for ships that run on fossil fuels today, the climate benefit could be significant, as similar hydrofoil technology could reduce fuel consumption by as much as 80%.
At the center of the research project is a unique measurement technique that the researchers have developed in order to understand in detail how hydrofoils behave in water when, for example, the load or speed increases or the positioning of the the hydrofoil changes. Using data collected from the experiments, the team developed and validated a method to accurately simulate and predict the behavior of the hydrofoil under various conditions. The method can now be used to develop hydrofoil design for electrically powered hydrofoil ferries.
The study was conducted in collaboration with the SSPA research center where lead author Laura Marimon Giovannetti works as a researcher and project manager. She has competed at elite level for the British and Italian National Sailing Teams. Today, she is a research and development advisor to the Swedish Olympic committee and the Swedish national team and her goal is to help the team win more medals at the 2024 Olympics. Marimon Giovannetti sees many possibilities for the unique measurement method developed by the team:
At the Americas Cup in San Francisco Bay in 2013, it was the first time we saw a 72-foot sailboat learn to “fly” using hydrofoils during the competition. And since then we have seen a huge increase in sailboats with hydrofoils. Thanks to this new method and this new knowledge, we are able to bring together a range of different branches of engineering – naval architecture, advanced materials and aeronautics as well as renewable energies.
—Laura Marimon Giovannetti
The growing popularity of hydrofoils and foiling boats can be explained by recent advances in composite materials, particularly in their strength to stiffness ratio. In general, hydrofoils have a very small wetted area compared to the wetted area of the hull. Thus, after the “take-off” speed, the wetted surface of the hull, and consequently the resistance of the boat, is considerably reduced. The greater the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be.
Current research investigates the interaction effects between the fluid and the structure of the Z-foil ZP00682 NACRA 17. The study is carried out both experimentally, in the cavitation tunnel of SSPA, and numerically using a viscous solver fully coupled with a structural analysis tool. The experimental methodology was used to validate the numerical tools, which in turn are used to reverse engineer the material properties and internal stiffness of the NACRA 17 sheet. The experimental flow velocity was chosen to represent realistic foiling velocities found in NACRA class 17, namely 5, 7 and 9 m/s. The forces and deflection of the Z-foil are studied, showing a maximum deflection corresponding to 24% of the submerged span. Finally, the effects of drift and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake configuration might be preferred in the search for minimum drag.
—Giovanetti et al.
Funding from Hugo Hammar of the SSPA and funding from Rolf Sörman of Chalmers University of Technology provided the financial support to conduct the experimental tests at the SSPA. This study also received funding from the Chalmers University of Technology Foundation for the Hydro- and Aerodynamics Strategic Research Project.
Marimon Giovannetti, Laura, Ali Farousi, Fabian Ebbesson, Alois Thollot, Alex Shiri and Arash Eslamdoost. (2022). “Fluid-structure interaction of a foiling machine” Journal of Marine Science and Engineering 10, no. 3:372.doi:10.3390/jmse10030372