Transforming MaK diesel powerhouses into low-emissions beasts

Thousands of MaK four-stroke, medium-speed engines in the global fleet will be capable of operating on methanol or ethanol, using newly introduced conversion kits from Caterpillar. Even with record levels of investment in alternative fuel-powered newbuilds over the last few years, just 7% of the global fleet by tonnage can use low- and zero-carbon fuels to support the reduction of CO2 and greenhouse gas (GHG) emissions. Two- and four-stroke enginemakers are developing solutions to retrofit the other 93% of the global fleet.

Caterpillar’s two new retrofit solutions are specifically designed to address a broad range of MaK four-stroke, medium-speed diesel engines in its engine portfolio that are widely used by passenger ships, ferries and container ships for propulsion and auxiliary power.

The kits enable the use of lower-carbon-intensity fuels such as methanol and ethanol, extending the service lives of existing vessels to comply with evolving IMO and EU emissions regulations. Using lower carbon-intensity fuels allows compliance with IMO and FuelEU Maritime GHG reduction targets and lowers carbon tax penalties under the EU Emissions Trading System (EU ETS) and UK Emissions Trading Scheme.

Green methanol, made using renewable energy, can reduce GHG emissions by 80 to 90% compared with traditional marine fuels.

Conversion to dual fuel

Existing MaK M 32 and M 43 engines would be converted into methanol and ethanol dual-fuel platforms using high-pressure direct injection (HPDI) technology. The HPDI technology, including specialised injectors and fuel supply systems, lets these long-stroke engine series operate on methanol or ethanol while maintaining diesel-cycle combustion principles. Caterpillar’s conversion concept requires only limited modifications to the existing engine hardware, reducing vessel downtime.

After conversion, the M 32 and M 43 engines will be capable of operating on 95% methanol or ethanol by volume, lowering GHG emissions by as much as 80% on a lifecycle basis, according to Caterpillar.

Blending technology

For its MaK medium-speed diesel engines spanning the model range M 20 to VM 43, the enginemaker has taken a different approach. Instead of converting these models to dual-fuel platforms, Caterpillar has developed special fuel-blending technology that achieves mixes of up to 35% methanol or ethanol with marine diesel oil (MDO), marine gas oil (MGO), or biofuel equivalents. An external blending module is paired with integrated monitoring and safety systems that allow the engines to use a mixture of conventional marine fuels with methanol or ethanol.

“M 32 and M 43 engines will be capable of operating on 95% methanol or ethanol”

GHG reductions with fuel blending can reach 20% for these engines, significantly extending the life of the vessel. Using fuel blending, operators can transition between methanol or ethanol and diesel, providing flexibility to support their annual fleetwide GHG reduction targets.

Sven Rosenow, Caterpillar’s global services director for MaK, said the retrofit kits will “empower MaK engine owners to continue operating the systems they trust while keeping pace with FuelEU Maritime requirements. Our alcohol-based fuel conversion kits help existing cruise, container, ferry and passenger ships to remain in service while reducing potential costs associated with IMO guidelines.”

Both conversions are delivered as OEM-engineered retrofit solutions, supported by Caterpillar and the global MaK dealer network, offering certified components and lifecycle service support.

Caterpillar said the exact duration of a conversion depends on vessel configuration, engine type, and the selected solution. “As with most major retrofit projects, conversions are typically planned to align with scheduled maintenance or shipyard periods to optimise uptime. The scope is engineered to reduce downtime through limited modification of existing engine hardware and a retrofit-focused design approach,” the company explained.

Extending the service life of an existing asset through a retrofit may prove a more commercially appealing option for a shipowner than investing in an alternative fuel-capable newbuilding.

Following installation, engine performance and maintenance intervals remain consistent to support ease of ownership.

Ethanol conversion in Brazil

The solutions were recently introduced as part of Caterpillar’s expanding portfolio for lower-carbon marine fuels, and discussions with customers and operators are ongoing as the industry evaluates pathways to decarbonisation.

As part of demonstration activities, Caterpillar is working with Brazilian offshore support vessel (OSV) operator Companhia Brasileira de Offshore (CBO) to validate ethanol blending conversion solutions under actual operating conditions.

At Nor-Shipping 2025, CBO announced its intention to retrofit a MaK M 32 C engine installed in one of its OSVs to operate on a blend of ethanol and diesel.