The maritime sector faces the challenge of reducing its pollutant emissions and optimising operating costs in the face of increasingly stringent environmental regulations. In this context, hybrid propulsion emerges as a technological solution that combines different energy sources to achieve more sustainable and efficient navigation.

In this article, we will analyse what hybrid propulsion is, how it works, its benefits for the shipping industry, and the future prospects for its large-scale adoption in ships and maritime vessels.

Context and definition of hybrid propulsion in the maritime sector

Concept and technologies used

Hybrid propulsion in ships combines traditional diesel engines with battery-based electrical systems and, in some cases, fuel cells. This approach allows energy sources to be alternated or combined to optimise performance, reduce fuel consumption and minimise pollutant emissions.

Examples of current hybrid ships

• Passenger ferries in Norway, such as the Ampere, a pioneer in electric-hybrid operation.
• Hybrid tugboats in the ports of Rotterdam and Los Angeles.
• Ro-Ro ships and cargo ships with dual systems combining diesel and high-capacity batteries.

Benefits for energy efficiency, emissions reduction, and operating costs

Impact on maritime sustainability

According to the International Maritime Organisation (IMO), maritime transport accounts for around 3% of global CO₂ emissions. The implementation of hybrid propulsion can reduce polluting emissions by up to 30-50%, depending on the type of vessel and route.

Fuel economy and operational efficiency

• Reduction in diesel consumption during low-speed operations and port manoeuvres.
• Lower maintenance costs thanks to the partial use of electric motors.
• Possibility of using renewable energy stored in batteries.

Success stories

Companies such as Stena Line and Color Line have reported significant fuel savings and emissions reductions after incorporating hybrid systems into their fleets.

Step-by-step operation of the hybrid system

Propulsion architecture

A hybrid system usually consists of:

1. Main diesel engine for open sea navigation.
2. Electric generators connected to high-capacity batteries.
3. Fuel cells (in advanced projects) for additional clean energy.
4. Intelligent control system that alternates and optimises the use of sources according to energy demand.

Practical example: hybrid Ro–Ro ferry

When leaving port, the ferry uses electric motors powered by high-capacity batteries, allowing it to manoeuvre silently and without polluting emissions in areas close to the coast, significantly reducing its environmental footprint and improving air quality for passengers and port communities. This mode also reduces underwater noise, benefiting local marine wildlife.

Once the open sea is reached, where environmental restrictions are less stringent, the main diesel engine is activated to maintain optimal cruising speed and ensure efficiency during the journey.

At the same time, the hybrid system intelligently manages the available energy, using part of the power generated by the diesel engine to recharge the batteries, preparing them for the next docking and departure manoeuvre.

In some Ro-Ro ferry models, this transition is fully automated, optimising fuel consumption and reducing wear and tear on mechanical components, which contributes to lower maintenance costs and more sustainable operation in the long term.

Common challenges and mistakes in implementation on ships

Technological barriers and initial costs

• High initial investment in battery systems and power electronics.
• Limited port infrastructure for electric recharging in some regions.

Common mistakes and how to avoid them

1. Undersizing batteries: this can lead to operational failures and reduced autonomy.
2. Not considering useful life cycles: long-term economic impact.
3. Poor system integration: loss of efficiency and cost overruns.

Lessons learned

Pioneering projects highlight the importance of energy planning, collaboration between shipowners, shipyards and technology suppliers, and the adaptation of crews to new operating methodologies.

Conclusions

Hybrid propulsion is emerging as one of the most promising solutions for advancing towards true maritime sustainability. With the ability to reduce emissions, improve energy efficiency and offer competitive advantages to shipowners, its adoption will continue to grow, driven by innovation and international regulations.

To learn more about this technology and other clean energy solutions in the marine sector, subscribe to our technical newsletter or contact us with any questions you may have about hybrid propulsion for ships.