Mermaid can reduce fuel consumption by more than 1,000 tonnes per year in some applications

Rina has unveiled Mermaid, a new hybrid propulsion concept designed to reduce vessel fuel consumption and emissions without locking shipowners into a specific fuel choice for the energy transition. The project is based on the idea of making greater use of the two-stroke main engine to enable it to serve as a primary source of electrical power for onboard services. Rina's architecture combines a shaft generator, a propeller shaft clutch and a battery system for energy storage.

The system is particularly advantageous during port stays

The system is particularly advantageous during port stays, which are often necessary for maritime transport. Once the propeller is disconnected, the main engine can continue to run in order to generate electricity directly or charge the batteries, which can then power onboard loads. This reduces reliance on auxiliary engines and enables the main engine to operate more efficiently.

Related: RINA awarded Approval in Principle to DRIFT Energy for its energy-harvesting ship design.

The design of Mermaid 

The design of Mermaid took the prevalent practice of "slow steaming" into account. Ships are spending an increasing proportion of their operational lives travelling at speeds lower than those for which they were originally designed. Integrating auxiliary engines with batteries enables the power output to be more closely matched to the actual operating conditions. This avoids the need for oversized engine capacity while maintaining an additional margin of safety and electrical resilience.

Rina's analyses 

Rina's analyses suggest that the system could potentially save over 1,000 tons of fuel per year in specific applications. Reduced consumption would also result in lower emissions and reduced costs associated with complying with future environmental regulations.

Mermaid is described as 'fuel-agnostic

The project's independence from the specific fuel used is a key feature. Mermaid is described as 'fuel-agnostic', enabling shipowners to implement a solution that is not dependent on a single prediction regarding the evolution of the energy transition.

"The issue that shipowners are currently grappling with," explained Antonios Trakakis, Technical Director of Energy Transition Solutions at Rina, "is not just about picking a fuel source. This is especially true given that future solutions might emerge that we are not even considering today. It's about preparing a vessel for a future that no one can predict with certainty. Ships ordered today will still be in operation in the 2050s, so decisions made now must remain commercially and technically viable for decades.”

Mermaid delivers short-term benefits

Rina says that Mermaid delivers short-term benefits by avoiding the need to design the vessel around a single decarbonisation scenario. ‘The Mermaid concept offers immediate operational and commercial advantages while reducing the need for costly future modifications. Rather than optimising ships for one specific decarbonisation scenario, it provides a flexible platform capable of adapting to evolving technologies, fuels and regulations.

’Related: RINA has approved SRC's Methanol Superstorage system.

Mermaid is designed to work with what the future holds.

Trakakis also said that there is currently no consensus on which fuels will dominate the future of shipping. 'Shipowners are presented with multiple potential pathways, each involving different risks and uncertainties. Mermaid is designed to work regardless of what the future holds. If the world changes, the ship is ready. If it doesn’t, the solution’s economics will remain sound.'

The concept's relevance

The concept's relevance extends to a diverse range of vessel types, encompassing tankers, bulk carriers, and container ships. Moving forward, this concept will be further elaborated through the development of a comprehensive technical design. Rina reports having already received positive feedback from shipowners and shipyards.

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