May 20, 2024

Scientists from Cranfield University in the UK are developing a kind of underwater wing for ships that could help decarbonise a sector responsible for more emissions than air travel.

Known as wave devouring propulsion technology, it is essentially a flapping foil system installed at the bottom of a ship’s hull that helps propel it along. Inspired by the tail fin of a whale, the system harnesses the kinetic energy of the waves to achieve propulsion without fuel.  

As the wing flows through the water, it automatically flaps up and down generating thrust — much like when a bird glides through the air or a fish cruises through the water.  

Just like a fish or a bird, however, the system won’t work unless there is an engine to provide initial power. But once a ship is cruising, the foils reduce the overall effort needed to push the boat forward.  

This graphic from Norwegian startup Wavefoil illustrates the basic concept:

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Lab-scale test models of the wave-devouring propulsion system at Cranfield’s ocean laboratory found it could reduce the fuel use of ships by up to 15%. While that might not sound all that much, it is a relatively simple technology that could be retrofitted onto existing vessels. In combination with the plethora of other technologies being developed to decarbonise shipping — like giant windwings or solar sails — the foils could help set the global shipping industry on course for net zero emissions. 

The concept of using flapping foils to generate thrust from flowing water was discovered and demonstrated by German researchers over a century ago. But for a long time, the process simply wasn’t well understood enough to scale on a practical level, and the urgency to cut fuel use wasn’t as great as it is today.    

Over the last few years, however, there have been a few attempts to commercialise wave devouring propulsion and bring it to market. Two companies, Wavefoil from Norway and Liquid Robotics from the US, have shown the most promise. 

Wavefoil made headlines in 2019 when it installed retractable bow foils on a ship for the first time in history. The giant fibreglass foils are designed to fold up into the ship’s hull when not in use, the first technology of its kind to do so. This means the foils can be retracted during heavy storms (they can withstand wave heights up to 6m, not more) and when docking. 

By harnessing the up and down motion of the waves, the foils help save fuel but they also increase comfort in rough seas, said their creators. Having raised €5mn so far (the latest round being a grant in 2022 from Innovation Norway), Wavefoil has installed its technology on several ships since its founding.