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Propulsion Systems: new ways of thinking about maritime transport for a greener world

30 September 2020
Article by Diego Moreira, development engineer at INEGI in the area of technologies for the sea

The global movement in search of greener solutions for the most varied types of systems is undeniable. Nowhere is this more evident than in the automotive sector, which is struggling with the electrification of the circulating car fleet as a sustainable alternative to internal combustion engines, aiming to reduce the emission of pollutants into the atmosphere.

The shipbuilding industry, in turn, also faces the same issues related to sustainability, although with different outlines. The current logistical transport model is linked to large vessels that consume huge amounts of fossil fuels, representing approximately 2.5% of global emissions of greenhouse gases (GHG or GHG) and 13% of emissions at the european level1.

Reversing this impact, however, requires a radical change from strongly established standards, which in turn generates several challenges, either in adapting to new technologies, or in the scale consumption of the resources necessary to make their implementation feasible, with the respective associated impact.

In this context, industry standards have been repeatedly altered, aiming to create a more sustainable model in the long term, in a strategy signed by the International Maritime Organization (IMO) to reduce GHG emissions by at least 50% until 20502. However, even with well-defined guidelines by the IMO, there is still no consensus on definitive solutions or a single technological line to be followed in terms of propulsion systems, in order to achieve the established goals.

Technological innovation is the engine of sustainability

The propulsion system is one of the most important systems on board, but the systems of large vessels have suffered very little change since the second half of the 20th century. The classic technology consists of the propeller set and four-stroke diesel engines, with some variants, namely the type of fuel used in order to meet the current pollutant emission standards, which tend to be more restrictive. The emergence of new technologies, however, is already translating into new solutions that promise to replace or assist this system.

The test of fixed sails or auxiliary wings stands out as a way of reducing consumption and harnessing wind energy to make transport more efficient, sustainable and less expensive. This type of solutions results in a reduction in fuel consumption of around 10% 3, and it is even possible to use with the base structures present in any large vessel, adapting the system to the existing fleet.

In the same context, through the Magnus effect, a concept widely known in fluid mechanics, rotating cylinders are also an efficient alternative. Known as rotor ships or Flettner ships (in honor of the German engineer who first explored the technology), these vessels emerged in the early 20th century in a purely conceptual way and are today timidly used in specific applications, with a potential for reducing consumption up to 25% 4.

Also in line with the objectives imposed by the IMO is the electrification of vessel engines, which, despite not having the space and load limitation common in the automotive industry, raises questions regarding autonomy versus the need for frequent recharging in port. The optimization of the ships' propellers (including new geometric shapes and unconventional arrangements) and propulsion based on water jets also produce noticeable gains in efficiency, but do not guarantee a drastic reduction of the ecological footprint in the sector, which will only occur with new ways of thinking about efficiency combined with energy use.

The 'clean' energy challenge

The challenge currently faced by companies in the sector is also a challenge assumed by INEGI. By leveraging competences in hydrodynamics, mechanical design and structure analysis, we intend to contribute to the development of alternative propulsion systems with the potential to favor the sustainability of the industry in the context of the blue economy, widely discussed in recent years5.

In this context, the development of technological solutions focused on the use of wave energy, both for the generation of electric energy and for the transmission of movement to vessels, also matters. The objective is to enable the production and use of 'clean' energy in a safe and economically competitive way.

Operating from submerged hydrofoils and with a bioinspired approach, this system is capable of absorbing energy from waves, an energy source widely available in the marine environment and completely renewable, ensuring the supply of electricity to subsystems, in addition to serving as main or auxiliary propulsion, depending on the size of the vessel.

Available since mid last century6, this type of technology has been increasingly explored, mainly in autonomous surface vehicles (USVs), with success cases that have even generated the interest of large economic groups7. However, as an auxiliary form of propulsion, a hybrid or dual system based on hydrofoils with energy recovery can increase the efficiency of large vessels, thus expanding the reach of the technology. In addition to the features already mentioned, the hydrofoil systems also guarantee gains in stability and reduced resistance, which in itself already improves the efficiency of the set as a whole, achieving promising results with zero carbon emissions.

The technology is maturing quickly, but there is still much to do before a model with a low ecological footprint within the shipping industry becomes a reality. In this sense, it is imperative that companies and institutions invest in R&D+i of systems aligned with such important objectives within the critical scenario in which we live. The future is blue, whether thanks to hydrofoils or sails that allow us to navigate to an increasingly sustainable world.

1. Reducing emissions from the shipping sector, Climate Action: European Commission.

2. P. Shallcross, U. Kleinitz, and S. Mueller, "Marpol Annex VI,” Superyacht Business, 2012.

3. Fixed Sail or Wings, Global Maritime Energy Efficiency Partnerships.

4. Rotor sail "E-Ship 1” saves up 25% fuel, ENERCON Press Release, 2013. 

5. The EU Blue Economy Report 2020, European Commission.

6. M. S. Triantafyllou, G. S. Triantafyllou, and D. K. P. Yue, "Hydrodynamics of Fishlike Swimming,” Annu. Rev. Fluid Mech., 2000

7. Wave Glider - Scalable and persistent monitoring for intelligent situational awareness, Boeing Company