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Boats that fly like the wind

A test model of a recreational boat is performed by a person in a marine environment.
Ivan Stenius gooses the throttle to bring the Foilcart test boat up to a speed of ten knots so that it can hydroplane, commencing ‘take-off’.
Published Jun 08, 2022

Silent zero-emission vessels that swiftly float past the cobs and skerries – is this the future of coastal and open-water boating? We paid a visit to the KTH Värmdö field station, where researchers are busy testing and developing an electric boat.

Behind a fence that surrounds the Djurö wastewater plant is a modular blue container building with ‘Djurö Marina Field Station’ inscribed on the sign. This is where innovative, sustainable maritime vessels are being built to explore the ocean – from the pelagic to the benthic realm and everywhere in between.

Just a stone’s throw from the Djurö Boating Club marina, KTH researchers Ivan Stenius  and Nicholas Honeth  are preparing to launch the Foilcart test boat – their silent, zero-emissions leisure and transport concept vessel.

One person is standing in front of two laptops that are placed on a test boat.
Before the boat is launched, the crew makes a few final adjustments to the steering controls.

The boat is rigged with advanced software, sensors, computers and a hydroplane foil, which allows it to hover gracefully above the water. This state-of-the-art technology reduces drag by 50–80 per cent – a necessity for electric propulsion.

“We get both higher speed and better range. One positive effect is that no waves are generated. It’s like riding first-class in a railcar – nice and peaceful,” maintains Mr Stenius, Research Director at the KTH Department of Vehicle Technology and Solid Mechanics.

Trimming the steering system

Thanks to the simplified hydrofoil design and lower manufacturing costs, the Foilcart is less expensive than similar electric boat options.

“That’s one of the points of our project. For electric boats to gain widespread acceptance, the prices have to come down to the level of ordinary boats,” acknowledges Mr Stenius.

A couple times a week, the researchers take to the sea to test out and improve the control system. They tweak the computer algorithms and trim the steering system to keep the vessel balanced during operation and counter the effects on the boat of waves, winds, weather and weight displacement.

Boat hull seen from below with rig, engines, rudders and propellers. In the background a person.
Under the hull lurks a hydrofoil, rudder and several electric engines.

The 3.5 metre-long vessel is fully equipped with microcomputers. Advanced sensors transmit control signals to the rudder based on readings that are taken 200 times a second.

Just before the day’s test run, Nicholas Honeth, an electrotechnology researcher, makes a few final corrections.

“It’s about several functions that control how the boat should lean on inner turns. I need to tweak the code a bit,” he says while looming over the computer screen waiting for the Foilcart to be lowered onto the water.

The ebb and flow of progress

When the neon-yellow vessel steals away with Mr Stenius at the helm, Mr Honeth makes himself comfortable in the ‘office’, a consort boat equipped with Wi-Fi, tracking computers and a heated cabin, which is moored today at the jetty along with the usual assortment of sailboats and speedboats.

In spite of several attempts, the boat fails to maintain its balance whilst rising above the surface. It rises and falls flat, several times in succession. The mystery’s revealed once they hoist the Foilcart up again with the crane – the elevator had loosened and now lies somewhere at the bottom of the sea.

Three leisure boats moored at a jetty. In two of the boats there is a driver.
From the consort boat (at left), Nicholas Honeth watches the test boat driven by Research Director Ivan Stenius as it gets ready to depart from the pier.

“Mechanical defects are highly unusual. But that’s how it is with experimental research – always a learning process,” acknowledges Mr Honeth.

The planned demonstration for financiers and stakeholders may need to be postponed a bit from the end of summer.

Chance to make a difference

“We’re about to introduce the world’s most compact hydrofoil system technology for boats. Once we’re able to get it to maintain its balance whilst hovering, we’ll be the first in the world with this concept,” says Mr Stenius.

Exactly when hydrofoil technology will gain widespread acceptance is anyone’s guess.

“In part, it’s all about demand and the public perception of ‘flying’ over water. If we can get businesses and other stakeholders on board, it should only be a matter of a few years before we can take the next step,” he says, adding:

“If we’re to reach the goal of a fossil-free society, maritime transport and the boating industry must also play a role. Hydrofoil technology offers the potential to really make a difference.”

Text: Christer Gummeson
Photos: Marc Femenia

Hydrofoil technology in brief

En testmodell av fritidsbåt färdas i vatten.
The Foilcart test boat ‘hydroplanes’ gracefully over the water. (Foto: SMaRC)

A hydrofoil is a type of ‘wing’ that is mounted beneath the hull of a boat. It lifts the entire boat above the surface to reduce friction with the water. The KTH boat, Foilcart, requires a speed just under ten knots in order to hover. The KTH researchers’ version of the hydrofoil has been simplified, with just one point of attachment on the hull. Their inspiration for the solution came from similar hydrofoils used in competitive surfing. Hydrofoil technology is nothing new, dating back over 100 years, but thanks to new advances in materials technology and electric boat design and improved electronic control systems, the technology has enjoyed renewed popularity.

Foilcart is part of KTH Baltic Tech Initiative  and is funded by the Swedish Transport Administration.

Belongs to: About KTH
Last changed: Jun 08, 2022