Marine diesel engines have gone through numerous innovative turns since being created by Frédéric Dyckhoff and Adrien Bochet in 1903 in France. Key advancements include the introduction of turbocharging in 1925 and fuel-injection pumps in 1927.
Recent innovation has been driven by concerns over the health and climate impacts of diesel fuel emissions. As a result, there has been a push to integrate a second, cleaner-burning fuel into standard diesel engine systems that, when used for combustion, produces fewer greenhouse gas pollutants. These efforts are contributing to the gradual development of dual-fueled workboats, both in the U.S. and globally.
The latest alternative to the traditional American diesel-fuel power package comes from Caterpillar’s newly introduced dual-fueled CAT 3500E with methanol as the second fuel. The CAT 3500E will be available in both 12-cylinder (up to 2,550 hp) and 16-cylinder (up to 3,386 hp) configurations. They are designed to deliver 100% of the power of the existing CAT 3500 diesels installed aboard tugboats, inland towboats, and offshore support vessels. So far, Caterpillar is the only company in this country known to have matched up methanol with diesel in a combustion engine.
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In preparation for a dual-fuel option, “[Caterpillar] looked at fuel capabilities and power densities,” said Will Watson, the company’s marine product director. “Methanol gives us the closest to being like diesel” for power density. Thus, with the two fuels closely matched, a boat’s “tank sizing [for methanol] and the amount of fuel needed on board is close” to being the same as diesel.
But, if the goal is to maximize total emissions reduction, you don’t want to fill a boat’s fuel tank with just any type of methanol. “The true benefit will come from green methanol,” said Watson, noting that a good portion of the methanol available today is not considered green. “You are not going to get the full life-cycle benefit [with conventional fossil-based methanol].”
Green methanol is produced from renewable sources or carbon capture, offering a lower carbon footprint. Compared with conventional methanol, which is derived from fossil fuels (primarily natural gas), green methanol often has a cleaner combustion profile, producing fewer pollutants.
Another advantage, Watson said, is that there’s not an overwhelming learning curve once a vessel owner adopts methanol as a second fuel. “The beauty of the fuel path we are going down, it’s probably the most efficient learning curve,” he said. It’s “not introducing huge amounts of differences of what owners, operators and mechanics are used to on today’s internal combustion engine. [The dual-fuel 3500E] is still an internal combustion engine.”
Watson noted that Europe and parts of Asia are ahead of the U.S. in developing the infrastructure needed to use green methanol for vessel propulsion. But even in those parts of the world, and certainly in America, what’s needed for a successful energy transition is more active infrastructures. “A lot of our discussion has been around the preparation and the readiness and the flexibility to accept the fuels when they become available,” he said. “The key thing is to be ready for it.”
Currently, there is no engine in the U.S. certified for dual-fuel use, Watson believes. Caterpillar’s 3500E has received DNV certification for a methanol-ready engine. “We are in the development process of bringing it to production,” said Watson. “That’s an early step in the journey to have production, which then comes with full certification.”
What type of workboat will the first dual-fuel CAT 3500E be powering? In all probability, it will go down in a tugboat’s engine room, for as Watson has noted in a previous article, the CAT 3500E has been optimized “to achieve high methanol substitution rates over a wide range of load factors, including the low load ranges that tugs operate in much of the time.” That reduces the greenhouse gases that might otherwise have been pumped into the atmosphere while providing the power a tug requires.
That first tug with a dual-fuel-powered CAT 3500E will be built at a Damen shipyard in Europe and will likely operate in the area it was built. “We plan to provide an engine in 2026,” said Watson. “Don’t know if it’ll be operational in 2026, but definitely in the next 18 months it will be in the water.”
“The tug segment, that’s where the focus has been,” he added. “Once we get this done, we’ll go onto other platforms.”
Shoring up supply
By Eric Haun, Executive Editor
A very small portion of the global commercial vessel fleet currently runs on alternative fuels: just 0.89% of vessels, or 3.37% in terms of gross tonnage (GT), according to the classification society DNV’s Alternative Fuels Insight (AFI) platform. However, the tides are turning as vessel owners, operators and charterers seek solutions to reduce their environmental footprint. Of all vessels on order, 17.43% (43.86% in GT) are being built to be powered by alternative fuels, DNV data show. Among these fuels, liquefied natural gas is leading the pack by a wide margin, followed in order by methanol, liquefied petroleum gas, hydrogen and ammonia.
Methanol burns more cleanly than diesel, resulting in lower emissions of carbon dioxide, nitrogen oxides, and particulate matter. Methanol is also readily available in ports worldwide, including in the eastern and southern U.S., where the fuel is commonly transported as a cargo.
“The U.S. is the country with second-highest production capacity in projects for e-methanol and bio-methanol, after China. There are also a few projects in Canada, so there is ongoing activity in North America,” said Kristian Hammer, senior consultant and AFI lead at DNV.
Dedicated methanol bunkering facilities do not yet exist in the U.S. — there isn’t a need yet — but because the fuel is commonly transported, some infrastructure is in place to support bunkering when the demand is there.
Today, most of the demand is driven by the large, oceangoing fleet. Danish shipping giant A.P. Moller-Maersk, for example, is investing heavily to build dual-fuel, methanol-capable containerships while also building out a green methanol supply chain to one day bunker these new vessels. According to DNV, 0.23% of the global fleet can run on methanol, while 13.68% of ships currently on order will have the capability to do so.
“Order uptake for methanol-fueled vessels and actual bunkering will increase the need for dedicated bunkering infrastructure and options in relevant ports,” Hammer said, “as well as ensure transportation and availability of methanol in these areas. Hence, oceangoing vessels will push for infrastructure and availability to be developed driven by the uptake.”
These efforts may ultimately support the workboat sector down the line as methanol engine technology advances and more market players begin to consider the fuel as an option for dredgers, crew transfer vessels, tugboats, and other harbor vessels.
For workboats, methanol, like diesel, is easy to carry, but it is less energy-dense, meaning more of the fuel is required. Another drawback is that it’s significantly more expensive, and renewable methanol is even pricier, though costs are expected to come down over time as supply chains mature. “Further tightening of regulatory and commercial drivers and incentives” is needed to help drive down prices, Hammer said.
