Researchers at Chalmers University of Technology, Sweden, have created a unique method for further developing hydrofoils that can significantly increase the range of electric vessels and reduce the fuel consumption of fossil-powered ships by 80%. An open-access paper on their work is published in the Journal of Marine Science and Engineering.

Hydrofoils, like wings, lift the boat’s hull above the surface of the water and allow the boat to travel with considerably less water resistance. In recent years, hydrofoils have revolutionized sailing, with hydrofoils making elite sailors’ boats fly over the surface of the water at a very high speed. The researchers at Chalmers and SSPA now want to enable the sailboats’ hydrofoil principle to be used on larger passenger ferries as well, resulting in major benefits for the climate.

Longitudinal balance of forces on a NACRA 17 foiling catamaran. Giovannetti et al.

The electrification of ferries cannot be done without drastically reducing their water resistance. This method will allow the development of new foil designs that can reduce resistance by up to 80%, which in turn would significantly increase the range of a battery-powered ship. In this way, we could also use electric ferries on longer distances in the future.

—research leader Arash Eslamdoost, co-corresponding author

Even for ships that today run on fossil fuels the climate benefit could be significant, as similar hydrofoil technology could reduce fuel consumption by no less than 80 per cent.

At the center of the research project is a unique measurement technique that the researchers have put together in order to understand in detail how hydrofoils behave in the water when, for example, the load or speed increases or the positioning of the hydrofoil changes. Using the data collected from the experiments, the team has developed and validated a method to simulate and predict with precision how the hydrofoil would behave under a variety of conditions. The method can now be used to develop the design of hydrofoils for electric-powered hydrofoil ferries.

The study was conducted in collaboration with the research facility SSPA where lead author Laura Marimon Giovannetti works as a researcher and project manager. She has competed at the elite level for both the British and Italian national sailing teams. Today she is a research and development adviser to Sweden’s Olympic committee and the Swedish national team with her sights set on helping the team win more medals at the Olympics in 2024. 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 sailing boat learning how to “fly” using hydrofoils during the competition. And since then, we’ve seen a huge increase in sailing boats with hydrofoils. With this new method and knowledge we are able to bring together a range of different branches of engineering – naval architecture, advanced materials and aeronautics as well as renewable energy.

—Laura Marimon Giovannetti

The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be.

The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway 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 set-up might be preferred in search for minimum drag.

—Giovannetti et al.

Hugo Hammar’s funding from SSPA and Rolf Sörman’s funding from Chalmers University of Technology provided the financial support to run the experimental tests at SSPA. This study also received funding from the Chalmers University of Technology Foundation for the strategic research project Hydro- and Aerodynamics.

Resources

• Marimon Giovannetti, Laura, Ali Farousi, Fabian Ebbesson, Alois Thollot, Alex Shiri, and Arash Eslamdoost. (2022). “Fluid-Structure Interaction of a Foiling Craft” Journal of Marine Science and Engineering 10, no. 3: 372. doi: 10.3390/jmse10030372