RINA's Mermaid Concept Turns Main Engine Into Power Source

New Concept Targets Auxiliary Engine Use

Classification society RINA has introduced a new propulsion concept called Mermaid, designed to reduce reliance on auxiliary engines by allowing a vessel’s main engine to generate onboard power. According to a press release covered by Ship & Bunker, the system combines a shaft generator, a propeller shaft clutch and battery storage integrated with the ship’s two-stroke main engine.

How It Works

Under the Mermaid setup, when a vessel is berthed in port, the propeller shaft can be disconnected from the main engine while the engine itself keeps running. In this mode, the main engine can supply electricity directly to the ship or charge onboard batteries. Those batteries can then continue supplying power even after the main engine has been shut down.

RINA said the arrangement is intended to lower bunker fuel consumption, reduce emissions, and cut operating costs, while making fuller use of the main engine rather than relying on separate auxiliary units for port power.

Fuel Savings and Slow Steaming Benefits

According to RINA’s analysis, the Mermaid concept could deliver fuel savings exceeding 1,000 metric tons per year in some applications, though the specific vessel types or operating profiles behind that estimate were not detailed. Beyond port operations, the system is also designed to help optimize propulsion during slow steaming, by more closely matching engine power output to actual sailing conditions rather than running at fixed settings.

Fuel Agnostic and Applicable Across Vessel Types

RINA describes Mermaid as fuel agnostic, meaning it is not tied to a specific fuel type and could be paired with various propulsion fuels as the industry navigates decarbonization pathways. The concept is intended to be applicable across multiple vessel segments, including tankers, bulk carriers and container ships.

Moving Toward Detailed Design

RINA stated it is now progressing Mermaid from a conceptual stage into a detailed design phase. The classification society noted this next step follows feedback gathered from shipowners and shipyards, suggesting early-stage industry input has already shaped the concept’s development before a fuller technical specification is released.

Apeks view — For owners and technical managers, the appeal here isn’t the concept sketch, it’s what detailed design will have to prove: real fuel-consumption data, integration risk with existing shaft generators and clutches, and maintenance implications across the vessel types RINA names. A 1,000-tonne savings figure without disclosed vessel profiles is a starting claim, not a benchmark. Verified in-service performance data, not press-release projections, should ultimately determine whether Mermaid earns a place in newbuild specifications.