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Hybrid bicycle-passenger ferry operates with low emissions using battery power and diesel propulsion during river trial

Electric and Hybrid Propulsion in the Maritime Sector

Author: Jeroen Berger • Publication date:

The maritime sector is entering a major transition. What was recently seen as experimental technology has now become a proven and practical way to power ships. Electric and hybrid propulsion systems make it possible to reduce harmful emissions, including carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM) and, depending on the fuel used, methane (CH4). These systems also help lower fuel consumption, reduce maintenance costs and decrease mechanical stress. This technology is no longer limited to pilot projects. It is already being used in many types of vessels, such as ferries on fixed routes, inland ships with swappable battery containers, harbor tugs that operate locally without emissions, and offshore vessels that use battery power to stay in position.

This shift is mainly driven by stricter regulations and growing pressure from the market. International rules, such as MARPOL Annex VI (2021) and the IMO’s EEXI requirements (2022), require ocean-going ships to show clear emission reductions. The European Union (EU) is adding even more pressure. Under the EU Emissions Trading System (EU ETS, from 2024), CO2 emissions come with direct financial costs. In addition, the FuelEU Maritime Regulation (2025) requires shipping companies and shipowners to switch gradually to fuels with lower greenhouse gas intensity. At the same time, national and local authorities are tightening their rules. Urban waterways are being declared zero-emission zones, ports are giving discounts on port fees for cleaner ships, and various funding and certification schemes are available to support investment in clean propulsion.

This article explains how electric and hybrid propulsion systems work, why they are urgently needed, how they are used in different types of vessels, and which regulations apply to their design, installation and approval.

What Is Electric and Hybrid Propulsion?

Electric propulsion uses electric motors powered by energy storage on board the ship. This energy is usually stored in lithium-ion batteries or, in some cases, generated by fuel cells that run on hydrogen or methanol. Because no combustion gases are released during operation, fully electric propulsion is especially suitable for areas with strict environmental rules, such as urban waterways, Natura 2000 zones and ports with emission limits.

Fully electric vessels produce no local emissions of CO2, nitrogen oxides (NOx), sulfur oxides (SOx) or particulate matter (PM). They therefore meet the highest emission standards, including those set out in MARPOL Annex VI (2021) and in national zero-emission regulations. With improved battery technology and the growing availability of shore-side charging infrastructure, more vessels can now operate without emissions on fixed and predictable routes. This is particularly the case for ferries, inland vessels and passenger ships, where emission reduction also leads to lower operating costs, less wear and quieter operation.

Hybrid propulsion combines electric motors with conventional combustion engines, giving ships more flexibility in how they use power. In a parallel setup, the electric motor and diesel engine work together. In a serial setup, the diesel generator provides electricity for the electric drive. In both cases, batteries play a key role by storing energy, covering peak power needs and keeping engine speeds steady. This results in better fuel efficiency and lower emissions.

Hybrid systems are especially useful for vessels with changing power demands, such as harbor tugs, offshore support vessels and dredgers. These ships can run on battery power during transit or while idling. When more power is needed, the diesel engine switches on, and the system ensures the engine runs at its most efficient level. This setup cuts emissions without requiring constant access to shore charging and serves as a realistic next step toward fully emission-free operations.

Technical Advantages and Maintenance Savings

Electric propulsion offers clear advantages when it comes to maneuverability, reliability and maintenance. Electric motors deliver full torque even at zero speed, making it possible to maneuver with high precision. This is particularly useful for ferries, tugs and tour boats operating in busy or confined waterways. Electric motors also require little maintenance. They do not need fuel filters or oil systems and produce very low levels of vibration. This reduces mechanical wear and helps keep vessels in service longer.

Hybrid propulsion systems provide an extra layer of efficiency. Batteries can handle short-term power peaks, allowing the diesel engine to run at a steady and efficient speed. This stability reduces engine stress, lowers fuel consumption per kilowatt hour and extends maintenance intervals. It also reduces the risk of technical issues under changing load conditions and supports a more robust and predictable operating profile.

In offshore operations, especially dynamic positioning (DP), hybrid systems offer major benefits. By using the electric part of the system strategically, generators can stay within their optimal load range. This prevents sudden or inefficient power changes and improves overall fuel efficiency. For example, in a hybrid platform supply vessel, DNV calculated that fuel consumption could be reduced by up to 15 percent, depending on the vessel’s operating profile and the time spent in DP mode.

Why This Transition Is Urgent Now

The pressure on the maritime sector to cut emissions is growing fast. International agreements and EU laws are setting stricter emission standards, both in technical design and in daily operations. Electric and hybrid propulsion systems offer a strong response to this challenge. Ships can meet current emission rules without the need for complex exhaust aftertreatment systems such as SCR catalysts or particulate filters, and without large-scale retrofitting.

Since January 1, 2020, MARPOL Annex VI, Regulation 14.1.3, has set a global sulfur limit of 0.50% m/m (mass by mass) for marine fuels. This applies to all vessels outside designated emission control areas. Inside Sulphur Emission Control Areas (SECAs), such as the North Sea and the Baltic Sea, a stricter limit of 0.10% m/m applies under Regulation 14.4 of the same annex.

Fully electric vessels meet these sulfur limits automatically, as they do not produce combustion gases. In hybrid systems, battery support allows the diesel engine to operate within its most efficient speed range. This lowers both fuel use and emissions of sulfur oxides (SOx) and nitrogen oxides (NOx), making compliance with MARPOL Annex VI technically achievable, even without using Exhaust Gas Cleaning Systems (EGCS, also known as scrubbers).

New rules also target energy efficiency and CO2 reduction. Since 2022, the Energy Efficiency Existing Ship Index (EEXI) applies to seagoing vessels over 400 gross tons (GT), setting minimum requirements for technical efficiency under MARPOL Annex VI. Adding battery capacity allows the main engine to be sized more efficiently, helping vessels meet their required energy index.

In 2023, the Carbon Intensity Indicator (CII) also came into force under MARPOL Annex VI. This applies to vessels over 5,000 GT and requires shipping companies to reduce CO2 emissions per ton-nautical mile of transport capacity on a yearly basis. Hybrid systems support this goal directly, especially during part-load operations and zero-emission maneuvering in port areas.

Financial incentives to reduce emissions are also becoming stronger. As of 2024, maritime shipping is included in the European Emissions Trading System (EU ETS), under Directive (EU) 2003/87/EC. The system applies to commercial ships over 5,000 GT that enter ports within the European Economic Area (EEA). Shipping companies and shipowners must pay for their CO2 emissions. From 2026, 100% of these emissions must be covered through tradable emission allowances. With market prices around 90 to 100 euros per ton of CO2, the cost of conventional propulsion can rise quickly.

In addition, the FuelEU Maritime Regulation (EU 2023/1805) requires commercial seagoing vessels over 5,000 GT calling at EU ports to gradually reduce the greenhouse gas intensity of their fuel from 2025 onward. The goal is a total reduction of 80% by 2050. Electric propulsion offers a clear advantage here, as it replaces fossil fuels and cuts operational emissions to near-zero levels.

With regulations tightening, economic pressure increasing and technology ready for use, electric and hybrid propulsion are no longer optional. For any stakeholder looking to operate sustainably in the coming years, this transition is not a future option, it is an urgent and necessary step.

Application by Maritime Segment

Electric and hybrid propulsion is no longer an abstract idea. It is a proven solution that is already in use across a wide range of ship types. While the level of electrification varies by segment, the technology consistently delivers strong results under real-world conditions. Its benefits are most significant on predictable routes, during part-load operation or in areas with strict emission limits. As a result, zero-emission or partially electric propulsion is increasingly becoming standard practice.

Ferries are leading the way in the shift to electric propulsion. The MF Ampere, which has been operating in Norway since February 16, 2015, was the world’s first fully battery-electric car ferry. With a 1 MWh battery pack, it saves around 1 million liters of diesel and avoids approximately 5,700 tons of CO2 emissions each year. Thanks to shore charging at both terminals, the vessel can fully recharge in ten minutes, clearly showing that electric propulsion is commercially and technically viable. A similar trend is underway in the Netherlands, where the Amsterdam public transport company (GVB) launched five zero-emission ferries on the North Sea Canal in 2021 and 2022. Each vessel is equipped with around 800 kWh of battery capacity, recharges in just three minutes per stop and operates entirely without emissions.

Inland shipping is also evolving, helped by short routes and frequent stops. A strong example is the Den Bosch Max Groen, the first fully electric container vessel using swappable 20-foot battery containers. These so-called ZESpacks are charged on shore using renewable electricity and immediately exchanged when empty. The expected annual emission reduction is 715 tons of CO2 and 13 tons of NOx. This ship is the first in a planned series of five identical vessels, enabling efficiency gains in charging infrastructure, logistics and fleet operations.

In ports, where air quality and noise have a direct impact on urban surroundings, hybrid tug deployment is growing rapidly. One of the earliest examples is in Rotterdam, where the RT Adriaan has been in service since 2012. This hybrid tug maneuvers entirely on battery power at low thrust, with the diesel engine only switching on when more bollard pull is needed. In practice, this results in about 30 percent fuel savings and a NOx reduction of around 50 percent. Shipbuilder Damen now supplies multiple hybrid ASD tugs (Azimuth Stern Drive) to ports including IJmuiden, Terneuzen and Den Helder. Port patrol vessels are also increasingly equipped with hybrid propulsion, allowing them to move through busy urban waters without emissions at low speed.

For platform supply vessels and other offshore support ships, hybrid technology has become essential. In dynamic positioning (DP) operations, power demand fluctuates constantly, making conventional generator control inefficient. Battery support allows generators to operate steadily at optimal speed while peak loads are handled by battery power. In real-world conditions, this leads to roughly 15 percent fuel savings, reduced emissions and lower engine wear. These benefits are being confirmed more and more often through class society assessments and operational data.

All of these examples show that electric and hybrid propulsion is not only environmentally sound but also economically feasible. Where the operational profile allows, this transition makes sense not just for sustainability, but also for compliance and long-term business continuity. The next step is scaling up, setting shared standards and achieving broader adoption across the sector.

Technical Validation and Safety

Introducing electric and hybrid propulsion systems on board ships involves more than just installing the technology. Verified performance and full compliance with strict safety standards are essential for achieving classification, certification and eligibility for policy support. Claims of fuel savings or emission reductions are only legally and technically valid if they are based on standardized measurement methods. Without such verification, performance data remain indicative and cannot be used in certification procedures, subsidy applications or Green Award inspections.

For sea trials, ISO 15016 is the global standard for measuring fuel consumption. It requires tests to be conducted under stabilized conditions, such as 75 percent of maximum continuous rating (MCR), calm weather, a clean hull and controlled loading. Only under these conditions can results be reliably compared between vessels and accepted by class societies or financiers.

Alongside trial measurements, long-term performance monitoring during daily operations is essential. ISO 19030 offers a standardized framework for assessing hull condition, fuel consumption and propulsion efficiency. This standard uses data from onboard systems, GPS and fuel flow meters to analyze trends in a consistent and objective way. Ships with electric or hybrid propulsion that aim to demonstrate long-term efficiency gains can rely on this method for results with near-laboratory accuracy.

In terms of safety, battery systems on board must meet specific additional requirements set by classification societies such as DNV, the American Bureau of Shipping (ABS) and Lloyd’s Register (LR). Battery compartments must include automatic fire detection and suppression, temperature monitoring at cell or module level and physical separation to prevent thermal runaway. The battery management system (BMS) must also include redundancy and fail-safe logic to ensure safety in case of system failure.

For battery systems operating at 690 volts or higher, extra safety training is mandatory. The so-called High Voltage Safety certificate is required for technical staff and crew members who work with high-voltage systems on board. This training covers electrical risks, emergency procedures and system operation, and is now included in the curriculum at several maritime training institutes.

When performance is validated according to standards and safety is properly certified, electric and hybrid propulsion become fully compliant options under maritime regulatory and classification frameworks. Only full compliance with these standards ensures access to approval, insurance and policy-related support.

Limitations and Preconditions

Although the advantages of electric and hybrid propulsion are clear, the technology also comes with certain limitations and preconditions. These are partly physical, partly infrastructural and partly related to risk management and long-term reliability. Successful implementation therefore requires careful assessment of vessel type, operational profile and operating environment.

For deep-sea shipping, fully electric propulsion is not currently feasible. The energy density of lithium-ion batteries remains limited: one ton of battery capacity provides between 0.5 and 1 gigajoule of usable energy, while the same mass of diesel delivers about 42 gigajoules. An ocean-going container vessel would require thousands of tons of batteries to achieve a comparable range, resulting in impractical weight, volume and charging times. For these types of vessels, hybrid propulsion or alternative fuels still offer the most realistic path to reducing emissions.

On shore, some of the required conditions are also not yet in place. High-power fast charging, for example, requires major upgrades to the electrical grid and standardized charging infrastructure. In seaports and logistics hubs especially, connecting to the high-voltage grid presents both technical and permitting challenges. The Megawatt Charging System (MCS), used in modular battery containers from Zero Emission Services (ZES), is an important step toward consistent and widely usable charging standards. This connector enables vessels to charge quickly at several megawatts, as long as the grid can supply enough capacity.

There are also safety and reliability issues that must be addressed in the design and operational phases. Battery systems are sensitive to thermal runaway, a rapid temperature increase in which heat from one cell spreads to others. As a result, precise monitoring of cell temperature and charge level is essential. Route changes or unexpected delays can also lead to range anxiety, or uncertainty about how far the ship can travel on its remaining battery charge. Furthermore, the long-term durability of batteries under maritime conditions, such as vibration, salt exposure and temperature shifts, is not yet fully understood. These factors affect system performance, maintenance frequency and total cost of ownership (TCO) over the life of the installation.

To manage these limitations properly, system design, installation and operational planning must be based on realistic assumptions, sound engineering and validation according to applicable standards. Only under these conditions can electric or hybrid propulsion be scaled up in a way that is technically reliable, economically viable and safe for long-term maritime use.

Policy Recommendation and Conclusion

For shipping companies, shipowners, technical managers and policy advisors, it is essential to implement electric and hybrid propulsion in a legally compliant, technically sound and strategically phased way. A successful transition begins with objective performance verification. Conducting sea trials in line with ISO 15016 and ensuring ongoing monitoring based on ISO 19030 provides a reliable foundation for performance claims, investment decisions and subsidy approvals. At the same time, installation must meet the requirements of classification societies, including battery safety, system integration and crew certification.

When applied correctly, electric and hybrid propulsion is legally compliant, technically validated and financially justifiable. The technology makes it possible to reduce emissions without major retrofitting and offers direct compliance benefits under MARPOL Annex VI, the EEXI, the CII and the EU ETS. At the same time, it delivers long-term business value through lower operating costs, reduced mechanical wear, quiet operation in emission-sensitive areas and increased residual value for vessels with zero-emission capability.

The maritime energy transition is no longer a future ambition but a current reality. Ships such as the MF Ampere, the Yara Birkeland and the Den Bosch Max Groen prove that electrification is not only technically achievable but also scalable across different types of operations. For those who invest today, clear advantages are within reach: better environmental performance, compliance with tightening regulations, access to emission-regulated markets and a lower total cost of ownership. The course has been set, and the momentum is growing. Moving forward means moving emission-free.

Frequently Asked Questions about Electric and Hybrid Propulsion in Shipping

In a diesel-electric setup, diesel generators produce electricity for electric motors that drive the propeller directly. While propulsion is fully electric, the energy source remains fossil-based. This system improves maneuverability and allows precise speed control but does not lead to structural emission reductions.

Hybrid propulsion combines two separate drivetrains: a mechanical drive (direct diesel) and an electric drive powered by batteries or a generator. This enables the vessel to operate electrically at low power and switch to mechanical propulsion under higher loads. The result is flexible performance across a broad power range.

This combination increases overall energy efficiency and allows emission reductions, particularly for vessels with variable operating profiles or frequent part-load operation.

The suitability of hybrid propulsion depends on the vessel’s operating profile, required power, and operational cycles. A complete system analysis is essential, supported by Computational Fluid Dynamics (CFD), which uses numerical flow models to map the vessel’s hydrodynamic performance. CFD provides insight into resistance, propulsion efficiency, and propeller-hull interaction, including under variable load conditions.

The outcomes of this analysis form the basis for sizing both the propulsion system and the battery package. By linking energy use to the desired zero-emission operating time, battery capacity, charging cycles, and system efficiency can be optimized. Combined with energy demand profiles, this approach offers a substantiated view of the technical feasibility, economic performance, and emission reduction potential of hybrid propulsion.

For inland vessels, harbor tugs, patrol craft and offshore support vessels, hybrid propulsion is often a viable solution, provided that battery capacity is optimized and appropriate charging infrastructure is available.

Initial investment in hybrid propulsion is typically 4 to 10% higher than for conventional diesel installations. The additional cost mainly results from the integration of battery storage, electric motors, and an energy management system. The battery system is usually the largest cost component. Depending on battery technology (such as lithium iron phosphate or nickel manganese cobalt), required capacity, and maritime safety requirements, system costs range from approximately EUR 250 to 1,000 per usable kilowatt hour (kWh).

Enhanced safety measures include fire detection systems, fire-resistant compartmentalization of battery rooms, and redundancy within the Battery Management System (BMS) to ensure continued functionality in case of failure. Large-scale applications using standardized battery packs can significantly reduce unit costs.

Hybrid propulsion reduces operating costs over time. By keeping diesel engines within an efficient speed range and compensating peak loads with battery power, specific fuel consumption decreases. At the same time, mechanical wear is reduced, resulting in longer maintenance intervals and improved vessel availability.

The average payback time for the additional investment is five to ten years, depending on factors such as fuel prices, sailing frequency, charging strategy and access to subsidies or environmental discounts. For vessels with high part-load operation, such as harbor tugs or inland ships with predictable routes, this payback period is often shorter.

Hybrid propulsion reduces mechanical load on diesel engines by maintaining operation within an efficient and stable speed range. This lowers wear on moving parts and extends maintenance intervals. Electric motors require minimal maintenance and do not need oil changes, fuel filters, or mechanical overhauls.

The Battery Management System (BMS) requires periodic inspection, including voltage monitoring, temperature control, and visual checks of each battery module. These tasks can usually be integrated into the vessel’s existing maintenance schedule.

Depending on operating time, sailing profile, and the share of electric propulsion, total maintenance costs are typically 15 to 30% lower compared to conventional propulsion systems.

Yes, hybrid propulsion can be technically combined with alternative fuels, as long as the combustion engine is designed or modified accordingly. In practice, hybrid systems running on HVO (hydrotreated vegetable oil), bio-LNG, GTL (gas-to-liquid), and methanol are already used in various vessel types.

This configuration further reduces the CO2 intensity of the overall propulsion system. It enables compliance with the FuelEU Maritime Regulation (EU 2023/1805), which requires a phased reduction in greenhouse gas emissions from vessels operating under an EU flag or calling at EU ports.

Using alternative fuels in a hybrid system also increases flexibility in energy management and fuel logistics. This is particularly relevant for shipping companies looking to prepare their fleets for future emission regulations and fuel supply reliability.

Yes, standardization is possible if the hybrid propulsion system is modular in design. By equipping multiple vessels with identical components for energy storage, charging interfaces, and power distribution, economies of scale can be achieved in maintenance, training, and spare parts management.

Software for energy management and system diagnostics can also be centrally configured, which improves reliability and operational readiness. Classification societies typically approve standardized systems more quickly if safety, EMC compatibility (electromagnetic interference control), and redundant fail-safes are in place.

Standardization is particularly relevant for shipping companies operating a homogeneous fleet or investing in series-built newbuild projects. It simplifies fleet operations and facilitates large-scale implementation of emission-reducing technologies.

Hybrid propulsion systems must be approved by a recognized classification society such as DNV, Lloyd’s Register, or Bureau Veritas. Approval requires verification of electrical integrity, power protection, battery safety, and fire prevention in line with current IACS Unified Requirements (such as E10 and M69) and additional class-specific guidelines.

High-voltage systems (>690 V) and lithium-ion battery systems are subject to further requirements for compartmentalization, detection systems, fire suppression, and Battery Management System (BMS) configuration. These measures are intended to prevent and mitigate risks such as thermal runaway, short circuits, and system failure.

If all requirements are met, hybrid propulsion does not negatively impact the vessel’s classification status. In many cases, it results in an additional class notation that acknowledges environmental performance, which can improve eligibility for port fee discounts or green financing.

Yes. Within the European Union and the Netherlands, various schemes are in place to support investment in sustainable propulsion for both seagoing and inland vessels. Tax incentives are available under the Environmental Investment Allowance (MIA) and the Random Depreciation of Environmental Investments (Vamil), specifically targeting environmentally friendly technologies such as hybrid propulsion.

In addition, the Green Deal for Maritime Shipping, Inland Navigation and Ports encourages the use of emission-reducing innovations, including battery-electric and hybrid systems. In specific cases, further subsidies may be available through the Sustainable Mobility Investment Framework (IKDM) or the Subsidy Scheme for Clean and Emission-Free Construction Equipment (SSEB), provided that the vessel’s use falls within the policy scope of mobility or construction logistics.

Several port authorities, including those of Rotterdam and Amsterdam, also offer environmental discounts on port fees for vessels with verified hybrid or zero-emission capability. To qualify for both subsidy and tariff benefits, performance validation based on standards such as ISO 15016 or ISO 19030 is required. In addition, technical installations must comply with the classification requirements of recognized class societies. Without this supporting documentation, fiscal or financial incentives cannot be granted.

Fully electric propulsion eliminates all local emissions, including CO2, NOx, SOx, and particulate matter. This provides clear benefits for compliance with environmental regulations, such as MARPOL Annex VI and national zero-emission zones. Electric propulsion is also quiet, vibration-free, and low-maintenance, which increases operational availability and improves comfort for crew and passengers.

Fully electric systems are particularly suitable for vessels with predictable operating patterns and regular access to charging infrastructure. Typical applications include ferries, inland cargo vessels, and passenger ships operating in urban waterways or near-port areas.

Fully electric operation is technically feasible when the vessel’s route and usage pattern are aligned with the available battery capacity and charging infrastructure. This is particularly the case for short, high-frequency routes with fixed docking points, such as ferry or inland waterway services.

Feasibility depends on several factors, including the energy density of the battery system, charging speed, available grid capacity at charging locations, and the number of charge cycles per day. The operational reliability and integration of the Battery Management System (BMS) are also key.

In practice, fully electric propulsion has proven effective in urban ferry services, container shipping using swappable battery units, and port-based vessels such as patrol boats, inspection craft, and supply vessels. When properly dimensioned and integrated into operations, fully electric systems provide a technically and legally compliant pathway to zero-emission shipping.