San Francisco Bay had the scoop of the world’s first flying sailboat. It was in 2013 for the 34th edition of the America’s Cup – the most prestigious sailing competition in the world. The Oracle team participated in a 22 meter long vessel that could fly over the water thanks to hydrofoils. Wing-like platforms attached to the underside of the hull. Since then, more boats have started using them. Now a Swedish team of scientists and engineers have found a method to design them as efficiently as possible so that ships can reduce their fuel consumption by as much as 80 percent.
Chalmers University of Technology and SSPA – a maritime knowledge company – have joined forces to research the interaction of hydrofoils with liquids. After a year and a half of research and testing, they found a method that would allow them to design better ship swings. Hydrofoil technology is not new. Their origins go back to the 1960s, when they were still made of steel. But the weight of the material and the maintenance it requires hampered its mass use. The current hydrofoils are made of carbon fiber, a lighter but more resistant alternative.
Laura Marimon Giovannetti – a former member of the British sailing team – is a senior researcher at SSPA. “Hydrofoils are similar to flying wings, but they are smaller because they perform their work in water. Water is 1000 times denser than air. They are designed to achieve the so-called ascent rate at which the hull is lifted out of the water. At that point, the only resistance is hydrofoil resistance. “
Reducing this resistance improves the efficiency of a vessel. The less power it has to counteract, the less energy it needs to sail. Current and future navigation technologies can thus benefit from the Swedish model, as they know what to expect from this important part and ultimately from the boat itself.
The calculation model considers the wings to be a flexible body. Therefore, the design must ensure that the same ‘lift’ is guaranteed in all scenarios. Otherwise the ship may not be stable.
“When the wing is deflected, the amount of lift we get is not the same as when it is not. The boat can then lose its flying advantages,” emphasizes Arash Eslamdoost, professor of applied hydrodynamics at Chalmers University of Technology.
The characteristics and payload of the boat are some of the most crucial aspects to consider. In addition to the forces that ships must be able to withstand, the nature of carbon fiber poses an additional challenge. The material consists of several layers, which ultimately influence the behavior of the wing. This factor also affects the relationship between load-bearing capacity and load-bearing capacity.
The SSPA test tunnel was the main test area for the hydrofoils. Circulating water is set to the desired speed. High-speed cameras record the images of the wing in the tunnel and measure the degree of deflection over time. “In this way, we were able to measure all the forces involved and balance the various components,” Marimon added.
The new thing about the method also lies in the fact that different measurement techniques are connected. Because wings are involved, knowledge of aviation was involved, as well as materials science. But the research at Chalmers Department of Mechanics and Maritime Science does not stop there.
“The design of hydrofoils must be reconsidered compared to conventional ships. For this purpose, we are also working on the development of propulsion systems for hydrofoils. In another ongoing project, we are developing a self-balancing system that detects movement on the boat and regulates sail height,” explains Eslamdoost.
The best test environment remains the open sea. Marimon used to sail in elite competitions – as a campaign for the Olympics in Tokyo 2020 – and she is well aware that sport has the potential to push new technologies to their limits. Sometimes such developments come as a surprise.
“The 2013 boats were not designed to fly. During the race, the sailors pushed the boat to its limits, so the catamaran started flying. Since then, more development has taken place. Sport brings the development of composite materials forward, making fibers stronger.”
Alternative to passenger ships
There are more and more varieties of hydrofoils, also for daily use. Hydrofoils will soon enter Swedish waters. The Stockholm region and the ferry manufacturer Candela have entered into a collaboration to deploy electric boats for public transport. The ships will carry the first passengers this year.
If the model works well, hydrofoils can be an alternative to reducing both traffic jams and CO2to reduce emissions in maritime cities. As battery technology continues to evolve – with lighter charging units – electric boat sailing will also benefit from this.