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Navigating the Green Seas: Biofuels and the Environmental Trade-offs in Maritime Propulsion


The maritime industry, responsible for transporting goods and people across the world’s oceans, faces a pivotal moment in its quest for sustainability. As the global community intensifies its focus on climate change, industries worldwide are urged to explore avenues for reducing carbon emissions. Despite the recreational marine sector’s relatively modest contribution to greenhouse gas (GHG) emissions, accounting for only 0.4% and 0.7% of carbon dioxide (CO2) emissions in the EU and USA transport sectors, the sector is proactively seeking ways to diminish its environmental impact.

With a growing emphasis on reducing carbon footprints, the choice of propulsion systems for vessels has become a focal point of debate. Contrary to popular belief, recent studies suggest that, for many vessels, using biofuels in traditional internal combustion engines (ICE) might be a greener alternative than opting for electric or hydrogen propulsion systems. In this article, we delve into the environmental implications of various propulsion choices and shed light on why sustainable synthetic or biofuels may hold the key to a more eco-friendly maritime future.

The International Council of Marine Industry Associations (ICOMIA), in collaboration with its decarbonization steering committee, enlisted the expertise of Ricardo PLC to conduct a thorough, third-party-reviewed Life Cycle Assessment (LCA). The study aims to identify and validate suitable propulsion technologies for decarbonizing recreational craft, aligning with broader environmental goals.

Aim: The primary objective of the study is to furnish objective data that guides strategic decisions and technology choices for achieving greenhouse gas reductions in marine leisure propulsion. In its report Pathways to Propulsion Decarbonisation for the Recreational Marine Industry, ICOMIA set out to create a robust analysis of the full environmental impact of all currently available propulsion technologies for recreational vessels under 24m. Ricardo, an independent research firm, investigated various propulsion technologies to help decarbonize marine leisure craft by 2035.

Approach: The study meticulously compares the viability of five distinct propulsion technologies—baseline fossil fuel Internal Combustion Engines (ICE), hybrid electric, hydrogen ICE or fuel cell, ICE with sustainable marine fuels (HVO and e-gasoline), and battery electric. The assessment encompasses nine representative recreational craft with hull lengths below 24 meters, ensuring a comprehensive representation of the global market.

The study covered boats from inflatable tenders with small outboards and personal watercraft up to large planing and displacement motor yachts (up to 24m), as well as sailing yachts, inland waterways craft, small powerboats, fishing boats and pontoon boats (a large sector in the US).

Factors considered include sales volume, engine power, and usage profiles to offer a meaningful overview. They analyzed nine boat types representing the global market, considering life cycle emissions, costs, usability, and future tech options.

To attain this, the analysis evaluates GHG life cycle emissions, costs, usability, range, and performance. Future technology and fuel availability are also taken into account, forming a holistic understanding of the overall suitability of different energy options for each craft category through 2035.

Practicality and Performance Conclusions:

Recreational craft necessitate diverse decarbonization technologies due to their unique characteristics, differing significantly from automotive vehicles. It notes that will 80% of a car’s environmental impact is in its usage (the rest being in its manufacture and delivery), a far higher proportion of a boat’s environmental impact comes from its manufacture – as high as 50%.

This is in part due to that fact that leisure vessels are used for a relatively tiny number of hours annually. Figures suggest that sailing yachts’ propulsion systems are used on average for jut 24 hours a year, while the boats have an average lifespan of 45 years. The environmental impact of electric propulsion increases dramatically when batteries need to be replaced

Hybrid systems and sustainable fuel ICEs can maintain range and power comparable to current baseline ICEs, with minimal impact on vessel displacement and onboard space.

Pure battery electric and hydrogen propulsion require substantial reductions in range and power to mitigate impacts on vessel mass, onboard volume, and purchase price.

The Case for Biofuels in Traditional Engines:

Lifecycle Analysis: Contrary to the prevailing narrative, a comprehensive lifecycle analysis reveals that for vessels with typical usage patterns, sticking with conventional internal combustion engines fueled by sustainable synthetic or biofuels such as hydro-treated vegetal oil (HVO) or e-petrol can significantly reduce the vessel’s global warming potential over its 45-year lifespan.

The most suitable propulsion system varies on a craft-by-craft basis, emphasizing the unsuitability of a one-size-fits-all approach. Recreational craft engines’ relatively low annual operating hours make it challenging for electric-only, hybrid, and hydrogen systems to outweigh higher production and maintenance impacts in the use phase. Internal combustion engines (ICEs) powered by renewable liquid fuels emerge as strong candidates, offering significant GHG savings, especially for low-utilization and long-lifetime craft.

Environmental Impact of Electric Propulsion: Surprisingly, the shift to electric or hybrid propulsion systems might increase a vessel’s global warming potential by over 35%. This is attributed to higher environmental impacts during the manufacturing of the yacht and its propulsion systems. The energy density of electric or hydrogen storage poses challenges, making it unrealistic to compare vessels with equivalent ranges or performance.

Energy Storage Challenges: A crucial factor in this comparison is the energy storage requirements. For instance, a small powerboat capable of covering 166 miles over 14 hours with fossil fuels would require 360% more energy storage by volume and 820% more by weight to achieve the same range when converted to pure electric propulsion. This drastic increase in storage volume and weight translates to a prohibitive 133% greater displacement.

Hydrogen Compromise: Even in the case of hydrogen storage, while a compromise can be made to retain vessel performance, the storage would still be 430% larger by volume and 350% more by weight compared to sustainable synthetic or biofuels.

Total Cost of Ownership Conclusions:

Sustainable drop-in fuel ICEs and parallel hybrid power systems are economically favorable for privately owned recreational craft.

Large marinas looking to fully decarbonize their fleets find better total cost of ownership (TCO) in hydrogen and sustainable fuel refueling infrastructure than electric charging stations.

Purchase price and operational costs increase for all propulsion technologies relative to baseline systems, with anticipated cost reductions over time as alternatives achieve market scale.

Environmental Considerations and Break-even Points:

Low-Usage Cases: Vessels with low-usage cases, including sailing yachts with an average annual usage of 24 hours under the engine, are unlikely to yield a reduction in greenhouse gases (GHG) over their lifespans with electric-only systems. Biofuels in traditional engines, however, show a potential for reducing global warming potential by around 35%.

Frequent and Prolonged Use: Boats in frequent and prolonged use may have a better chance of reaching the break-even point with electric or hydrogen systems. However, the environmental impact heavily depends on the specific usage patterns of the vessel.

Hybrid Systems: Hybrid systems, combining conventional and electric propulsion, may, in some cases, offer the greenest option. Striking a balance between sustainability and performance, these systems aim to provide efficient and eco-friendly maritime solutions.


While the maritime industry seeks greener alternatives for propulsion, the choice between biofuels in traditional engines and electric or hydrogen systems is not a one-size-fits-all scenario. The environmental impact heavily depends on the vessel’s usage patterns, energy storage requirements, and the specific technologies employed. As the industry navigates these complexities, a nuanced understanding of the trade-offs is crucial to making informed decisions that steer us toward a more sustainable and eco-friendly maritime future.

The journey to cleaner seas requires ongoing tech upgrades. More efficient batteries, hydrogen fuel cells, and low-carbon fuel production are the life jackets the industry needs to stay afloat. Infrastructure needs a facelift too, with wider availability of hydrogen and electric charging stations for boats becoming essential docking points. Finally, clear policy directions are like a trusty compass. The industry needs supportive policies that acknowledge the sector’s diversity and encourage a whole fleet of decarbonization solutions to navigate a sustainable future for recreational boating.


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