01 Mar 2024
by Dr Sam Andrews

Propelling change in shipping decarbonisation

With the ongoing emphasis on decarbonisation and energy transition in the shipping industry, we look at two alternative and supplemental propulsion systems in and above the water.

The effectiveness of any alternative propulsion system lies in its ability to convert naturally-generated energy into thrust. In the ocean, one of those energy sources is waves.

To harness this power, Dr Liang Yang, Lecturer in Marine Renewable Energy Systems at the Centre for Energy Engineering, Cranfield University, looked to an uncommon propulsion system: flapping hydrofoils.

The idea of using flapping-based propulsion, which draws its inspiration from the natural world, is not new.

“We have engineered propellers, which are very efficient, but animals generate thrust by flapping a tail, a wing, for example,” explains Yang.

Flapping-based propulsion systems can be found on uncrewed surface vessels, such as wave gliders. These hydrofoils move passively with the motion of waves, generating propulsion. Yang says it wasn’t clear whether this ‘wave-devouring propulsion’ could be applied to larger vessels.

There are many aspects to consider. “We needed to understand the theory so we could design all the elements of the system, so we spent a long time investigating the physics behind this type of system,” says Yang.

There are also design elements questions to explore. “’What size foil for a particular size or shape of a vessel moving at a particular speed?’ ‘How many foils should we use and where should they be placed?’ ‘Should they be rigid or flexible?’” Yang reasons.

Research published by Yang and colleagues last year in Renewable and Sustainable Energy Reviews and this year in Physics of Fluids suggests that the wave devouring propulsion systems could see vessels saving some 10-20% on fuel costs.

“As long as there are waves, we can use them to generate thrust in the direction we want, it doesn’t matter what the wave direction is,” says Yang.

Above the water: updating an old propulsion system

Arguably, the oldest propulsion system that harnesses natural energy is in the form of sailing boats. Now, a Horizon Europe-funded (EU’s funding programme) partnership of eleven European universities and maritime companies have come together to develop the world’s first wind-powered roll-on roll-off (ro-ro) vessel.

Rather than using traditional sails, the Orcelle Horizon project looks to use stiff wing sails that can be rotated 360 degrees and tilted down.

“It’s motorised sailing that we’re looking into. So, when the wind conditions are favourable, vessels can use the wind. When conditions are not favourable, they can go back to conventional systems,” explains Emil Kotz, Manager of Customer Projects at Oceanbird, which designs and builds the wing sails.

“Wind conditions between the Atlantic, Mediterranean, and other areas are very different, so it’s not a given that we can use wind power everywhere,” confirms Lars Ekren, Senior Manager/Naval Architect of Newbuildings and Conversions at Wallenius Wilhelmsen.

The team is currently working on retrofitting an existing vessel: the Wallenius Wilhelmsen-owned Tirranna with a single wing.

“One of the challenges with the retrofit is structural integration. You have vessels optimised for their intended cargo. They weren’t built with the intention of putting something that delivers high forces on top of the vessel,” Kotz says.

Alongside the Trianna, the team is building a land-based prototype. Together, they will allow the team to test the performance, efficiency, and safety of these systems, as well as use them for training.

“After testing and learning, we will create a newbuild: the Orcelle Wind,” says Ekren.

While the team is aiming for efficiency gains of 5-10% with the single-sail Trianna, it is hoped that this purpose-built 220-metre-long multi-wing demonstrator ro-ro vessel will achieve efficiency gains of 50%.

“The key to the success with this is the very good collaboration we have with everyone in the project,” says Ekren. “It’s something very new to all of us.”

Main image: concept image of main sail and flap; credit: Oceanbird