Anemoi and NACKS Win ClassNK Approval for Rotor Sail Designs Targeting Ultramax Boom

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Anemoi Marine Technologies and Nantong COSCO KHI Ship Engineering Co. Ltd (NACKS) have secured approval in principle from ClassNK for two rotor sail integration designs tailored to the Ultramax bulk carrier segment, positioning the partners to capture demand as the 60,000 to 65,000 DWT fleet enters a period of rapid newbuild growth led by Chinese yards.

The AiP covers two configurations using Anemoi’s latest generation rotor sail, measuring 3.5 metres in diameter and 24.5 metres in height. One arrangement places a single sail on the forecastle deck. The other deploys three sails along the upper deck on a longitudinal rail system. Both designs offer a larger sail area than the unit Anemoi fitted on its pilot Ultramax installation in 2018, aiming to deliver greater fuel savings on a vessel class that accounts for a significant share of global dry bulk tonnage.

The timing is deliberate. China now accounts for more than 25% of bulk carrier newbuilds, up from roughly 5% a decade ago, according to DNV data. NACKS, part of the COSCO Shipping group, is among the yards contributing to that expansion. By partnering with a COSCO owned builder, Anemoi gains a direct route into the Chinese shipbuilding ecosystem at a moment when yards there are filling order books with next generation bulk tonnage.

Nick Contopoulos, chief commercial officer at Anemoi, said the AiP builds on lessons learned since the company equipped the M/V Afros in 2018, the first bulk carrier in the world to operate with rotor sails. The new designs apply that operational experience to Anemoi’s third generation products, optimising installations for maximum efficiency.

ClassNK’s review assessed sail particulars and arrangement, foundation and supporting structures, initial trim and stability calculations, fire and safety provisions, and energy efficiency performance under the International Maritime Organization‘s Energy Efficient Design Index (EEDI) framework. The EEDI sets minimum efficiency standards for newbuild vessels, making wind assisted propulsion an increasingly attractive compliance tool as thresholds tighten in the years ahead.

The single sail forecastle configuration is designed for operators seeking a lower capital entry point or those whose cargo operations limit available deck space. The three sail rail system targets owners willing to invest more upfront in exchange for proportionally higher fuel and emissions reductions across a voyage.

Ultramax carriers were among the earliest commercial adopters of wind assisted propulsion technology, and the segment’s combination of size, trading pattern, and relatively open deck geometry makes it well suited to rotor sails. As regulatory pressure mounts through instruments such as the EEDI, the Energy Efficiency Existing Ship Index (EEXI), the Carbon Intensity Indicator (CII), the EU Emissions Trading System, and FuelEU Maritime, owners ordering new tonnage face growing incentive to specify fuel saving technologies at the design stage rather than retrofitting later at higher cost.

The AiP does not guarantee a construction order, but it signals to shipowners and charterers that the integration concepts meet classification standards and can move toward detailed engineering with reduced technical risk. For NACKS, the collaboration adds a proven wind propulsion option to its portfolio as it competes for Ultramax contracts in a market where environmental credentials increasingly influence procurement decisions.

Anemoi’s rotor sails use the Magnus effect, spinning cylinders that generate forward thrust when wind crosses the vessel’s beam, to cut fuel burn and associated greenhouse gas emissions including CO₂, SOx, and NOx. The company holds classification approvals across multiple societies and has completed installations on several vessel types beyond bulk carriers, including chemical tankers.

The partnership reflects a broader industry pattern in which technology providers are embedding their systems into shipyard design catalogues early, ensuring that wind propulsion is treated as an integrated engineering solution rather than an aftermarket addition.