Methanol four-stroke engines ready for first installations

Engine technology has been developed to enable tugboats and workboats to operate on methanol fuel, while experience with biofuels shows these are being safely combusted to reduce pollutants in ports and along coastlines.

Caterpillar, which celebrates its centenary in 2025, gained class approval for its methanol-ready marine main and auxiliary engines in November 2024. DNV granted an approval in principle for the Cat 3500E series of engines, which are available in 12-cylinder (up to 1,901 kW) and 16-cylinder (up to 2,525 kW) configurations.

Class-approved engines are now available for newbuild and repower projects, and upgrade kits for existing Cat 3500E engines, facilitating the use of methanol fuels. Tug owners will now be able to comply with strict emissions standards under IMO Tier III and IMO SOLAS rules for maritime deployment.

Delivered with a turbocharger and servicing hatches, new options such as a closed crank-case ventilation system are offered, which enables exhaust to be recycled instead of vented, and fuel coolers, heat exchange and oil-mist detectors.

The first set of methanol dual-fuel Cat 3500E marine engines to be installed are expected to go into newbuild tugs Damen Shipyards will be constructing for completion in 2026, under agreements signed during Riviera’s 27th ITS Convention in Dubai in May 2024.

Caterpillar has already successfully leveraged innovative dual-fuel technology across several industries that are already using alternative fuels to diesel, says Caterpillar Marine product manager Will Watson.

“Methanol will play an important role in the maritime industry’s energy transition efforts, and we will provide vessel owners and operators with high-quality methanol solutions,” he says.

Caterpillar is exploring other alcohol-based fuels such as ethanol for use in markets where there is high availability, for example in Brazil, he tells Riviera. The US-headquartered original equipment manufacturer has also started testing these fuels in Cat 3500E engines.

Tugs and workboats operating on alcohol-based fuels need different storage and handling configurations, designs and technologies than those using conventional fuels, requiring a collaborative approach to development and trials.

“We are talking with designers and shipyards to be fuel-flexible and ready, so when owners want to make the move, the vessel is prepared and our engines are ready,” says Mr Watson.

He expects a multi-fuel future for tugboats and workboats, with the transition happening at different paces in various regional markets. “Building flexibility is key for being ready for what is coming.”

For now, more owners are using hydrogenated vegetable oil (HVO) fuels and blends of fatty acid methyl ester (FAME) with diesel in main four-stroke high-speed engines.

“HVO is a drop-in fuel, a substitute for diesel and our engines perform the same, ie like-diesel performance and maintenance,” says Mr Watson. Cat engines also run on FAME and biodiesel blends. “Our engines can run on B100 and lower levels (B20), even with exhaust aftertreatment. But handling biofuels is another layer for owners to consider.” 

There are challenges with storage and biofuel processing, which can be overcome on shore and on board vessels.

“If someone wants a quick step in their transition journey, biofuels are viable and cost-effective, with some reductions in lifecycle emissions, lower NOx and particulates. It is a good and easier step,” says Mr Watson.