Classification society and engineering consultancy RINA has unveiled a ship propulsion concept called Mermaid, designed to help shipowners reduce fuel consumption and lower emissions while maintaining flexibility as the maritime industry's decarbonisation trajectory continues to evolve.

The concept expands the role of a vessel's two-stroke main engine beyond propulsion, according to RINA, enabling it to serve as the primary source of onboard power and reducing reliance on auxiliary engines. Mermaid combines a shaft generator, propeller shaft clutch and battery energy storage in a propulsion architecture that is claimed to improve efficiency without committing owners to a specific fuel pathway.

When a vessel arrives in port, the propeller is disconnected while the main engine continues generating electrical power. Rather than depending on auxiliary engines to meet onboard demand, Mermaid is said to enable the main engine to supply electrical power directly or charge the batteries. Once charged, the batteries provide onboard power, allowing the main engine to operate at reduced load, cutting fuel consumption and emissions.

The concept also addresses operational conditions arising from slow steaming, which has become more common across major shipping segments. By combining auxiliary engines with battery energy storage in a hybrid propulsion arrangement, the design claims to better match propulsion power to real-world operating conditions, reducing the need to install excess engine capacity while providing an additional source of electrical power.

According to RINA's analysis, Mermaid can reduce fuel consumption by more than 1,000 tonnes per year in certain applications. The company also claims the batteries may deliver safety benefits by enhancing onboard power resilience and reducing the risk of power loss during critical operations.

Antonios Trakakis, energy transition solutions technical director at RINA, noted: "The challenge facing shipowners today is not simply choosing a fuel, particularly as future solutions may emerge that we are not even considering today. It is preparing a vessel for a future that nobody can predict with certainty. Ships being ordered today will still be operating well into the 2050s, so today's decisions need to remain commercially and technically sound for decades."

Trakakis added: "Today there is no consensus on which fuels will dominate the future of shipping. Owners are being presented with multiple possible pathways, each carrying different risks and uncertainties. Mermaid was designed to work whatever the future brings. If the world changes, the ship is ready. If it does not, the economics still work."

RINA says the concept is applicable across a range of vessel types, including tankers, bulk carriers and container ships. It is currently being developed into a fully detailed design following what the company describes as encouraging feedback from shipowners and shipyards.