Shipping has been a relatively fuel-efficient sector: moving 90% of global trade at a cost of just 3% of CO2 emissions. But the 2050 target for maritime decarbonisation in the UK has meant a whole new regime of pressures and some severe challenges ahead. Members of the International Maritime Organisation have committed to reduce CO2 emissions across international shipping by at least 70% by 2040.
The scale of the industry and its capital infrastructure mean introducing changes to reduce emissions come with a vast cost. Meanwhile, of course, its an infrastructure that's growing fast around existing, fossil fuel-based technologies. Ever-growing volumes of traffic mean that instead of being cut back, carbon emissions in the sector are estimated to triple by 2050. The UK’s industry alone has called for £2 billion in investment annually to deliver zero-carbon changes needed. In the meantime, there are no currently available technologies for the marine industries — electric or hydrogen etc — that can simply be introduced as an alternative.
In this context, piecemeal engineering design technologies that can deliver short-term savings in fuel use and emissions become increasingly important.
It has been known for years that marine vessels with a specially-adapted hydrofoil can be partly or fully propelled by ocean waves — similar to how fish (or, with more similarities to shipping, a whale) makes use of its fin. In this way, wave energy can be converted directly into thrust forces. Research at Cranfield has looked at how a bio-inspired foil can best be designed and implemented to maximise levels of propulsion and save on fuel use, whether the fossil fuels still currently in use, or the new generations of sustainable fuels.
Work on lab-scale test models of a ‘wave-devouring propulsion’ (WDP) design in Cranfield’s Ocean Systems Test Laboratory has demonstrated the potential to reduce fuel use by 20%; this, in turn, would mean up to 15% reduction in carbon emissions from fossil fuels per ship, depending on the size of the ship and wave conditions. WDP technology has also been tested with small vessels, such as a Suntory Mermaid II, a wave-powered boat that successfully completed a 110-day voyage from Honolulu, Hawaii to the Kii Channel. Current plans suggest that the technology should be available for use by industry within five years.
The research project includes supporting studies into how wave energy can be optimised for cargo vessels. This means design features that allow the substructure to adapt to changing weather and wave conditions, how different sizes of ship behave in these different conditions, and how more active propulsion can be generated through movement of the fin-like hydrofoil. There is also attention being paid to how cargo vessels can follow the best wave routes around and between coastal areas, allowing WDP to have the greatest impact.
WDP is a simple enough idea, but one that hasn’t been introduced previously because the science of the mechanism of wave-devouring propulsion wasn't well understood; and the imperative of fuel-savings wasn't so intense. The use of WDP is a low-cost means of reducing fuel use because it involves the addition of a sub-structure onto existing vessels with no need for expensive adaptations of engine machinery or related fuel systems. The foil can be fitted at the bow of the ship for passive propulsion, making use of the ship's motion; or it can be used as an active flapping foil propulsion system to increase the efficiency and reduce the noise. WDP can also be used in a hybrid form alongside wind propulsion technologies to deliver further fuel savings.
Also, the effectiveness of the new WDP model means that small unmanned surface vessels, used for oceanography, waste collection and environmental monitoring as well as transporting limited amounts of cargo, would be wholly self-powering, and could remain at sea indefinitely.
One of the UK’s richest natural assets has always been its wave power. But as a straightforward means of generating electricity the offshore infrastructure and maintenance involved has always been too expensive a proposition for serious implementation. WDP will be one way of making sure that an endlessly sustainable natural resource is harnessed for the good of the wider environment and industry.
Dr Liang Yang is a Lecturer in Marine Renewable Energy Systems at Cranfield University's Centre for Energy Engineering