Powering the Voyage: Engines, Fuel, and the LNG Shift
If you’ve ever stood on a dock watching a Ro-Ro car carrier glide into port, you might not give much thought to what’s happening below deck. But beneath those towering stacks of vehicles lies the beating heart of the ship: its propulsion system. For decades, that heart ran on heavy fuel oil (HFO)—a thick, tar-like residue left over from refining crude oil. It was cheap, energy-dense, and, until recently, the undisputed king of maritime fuel. But like a diesel-guzzling muscle car in an age of electric Teslas, HFO’s days are numbered. The shipping industry is in the middle of a fuel revolution, and at the center of it is liquefied natural gas (LNG).
The Heavy Fuel Oil Era: Power at a Price
For most of the 20th century, HFO was the workhorse of global shipping. It’s what powered the engines of everything from container ships to bulk carriers—and, of course, the massive pure car and truck carriers (PCTCs) that ferry millions of vehicles across oceans every year. The appeal was simple: HFO was abundant, cheap, and packed with energy. A single Ro-Ro could burn through 50 to 100 tons of the stuff per day, depending on its size and speed, and still turn a profit.
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But that power came with a cost—one the world is no longer willing to pay. HFO is one of the dirtiest fuels on the planet. When burned, it releases a cocktail of pollutants: sulfur oxides (SOx), nitrogen oxides (NOx), particulate matter, and, most critically, carbon dioxide (CO₂). The International Maritime Organization (IMO) estimates that shipping accounts for nearly 3% of global CO₂ emissions—more than the entire country of Germany. And HFO is a big reason why.
“Heavy fuel oil was never designed with the environment in mind,” says Lars Robert Pedersen, Deputy Secretary-General of the Baltic and International Maritime Council (BIMCO). “It was a byproduct of refining, and for a long time, the industry treated it like a necessary evil. But as regulations tightened and public pressure grew, it became clear that we couldn’t keep burning the stuff forever.”
That pressure came to a head in 2020, when the IMO’s global sulfur cap slashed the allowable sulfur content in marine fuels from 3.5% to just 0.5%. For Ro-Ro operators, this was a wake-up call. Either they switched to low-sulfur fuel oil (LSFO), installed exhaust gas cleaning systems (scrubbers), or found an entirely new fuel source. Many chose the first two options—at least temporarily. But the writing was on the wall: HFO’s reign was ending.
The LNG Revolution: Cleaner, But Not Without Challenges
Enter liquefied natural gas (LNG). If HFO is the diesel-guzzling pickup truck of marine fuels, LNG is the hybrid SUV—cleaner, more efficient, but with its own set of trade-offs. When burned, LNG produces virtually no sulfur oxides, 85% fewer nitrogen oxides, and up to 25% less CO₂ than HFO. For an industry under pressure to decarbonize, those numbers are hard to ignore.
“LNG isn’t a perfect solution, but it’s the best bridge we have to a zero-emission future,” says Mikael Karlsson, Head of Sustainability at United European Car Carriers (UECC), one of the first companies to adopt LNG-powered car carriers. “It buys us time while we develop truly carbon-neutral fuels like ammonia or hydrogen.”
UECC’s Auto Eco and Auto Energy, two of the world’s first LNG-powered PCTCs, are prime examples of this shift. These ships, delivered in 2016 and 2017, can run on either LNG or traditional marine gas oil (MGO), giving them flexibility as bunkering infrastructure evolves. Since then, other major players have followed suit. NYK Line’s Sakura Leader, delivered in 2020, was the first large-scale LNG-powered car carrier in Japan, capable of carrying 7,000 vehicles while cutting emissions dramatically. Meanwhile, Wallenius Wilhelmsen has ordered a fleet of LNG-ready vessels, with plans to transition fully to LNG as fuel availability improves.
But LNG isn’t without its challenges. The biggest? Space. LNG is stored at -162°C (-260°F) in specialized, heavily insulated tanks. These tanks take up valuable real estate—real estate that, on a car carrier, could otherwise be used for cargo. On a typical PCTC, LNG storage can reduce carrying capacity by 5-10%, depending on the ship’s design. For operators already squeezed by tight margins, that’s a tough pill to swallow.
“Every square meter on a car carrier is optimized for revenue,” explains Captain Anna Bergström, a veteran Ro-Ro master. “When you add LNG tanks, you’re essentially sacrificing space that could hold 200-300 extra cars. That’s a direct hit to the bottom line, especially on long-haul routes where fuel consumption is highest.”
Then there’s the cost. LNG-powered ships are 20-30% more expensive to build than their HFO counterparts, thanks to the need for specialized tanks, fuel systems, and safety measures. And while LNG is often cheaper than low-sulfur marine gas oil (LSFO), its price can be volatile, tied to the same geopolitical whims that roil natural gas markets. The 2022 energy crisis, triggered by Russia’s invasion of Ukraine, sent LNG prices soaring, leaving some shipowners questioning whether the switch was worth it.
Finally, there’s the infrastructure problem. Unlike HFO, which can be bunkered almost anywhere in the world, LNG requires specialized terminals. While Europe and parts of Asia have made strides in building LNG bunkering hubs, many ports—especially in developing regions—still lack the necessary facilities. This forces LNG-powered ships to plan their routes carefully, sticking to corridors where fuel is available. For a global industry that thrives on flexibility, that’s a major constraint.
Hybrids and Scrubbers: The Middle Ground
Not every shipowner is ready to go all-in on LNG. For some, the answer lies in hybrid solutions—engines that can run on multiple fuels, giving operators the flexibility to adapt as regulations and markets evolve.
The most common of these are dual-fuel engines, which can switch between LNG and traditional marine fuels like MGO or LSFO. These engines offer the best of both worlds: the emissions benefits of LNG when it’s available, and the reliability of conventional fuels when it’s not. MAN Energy Solutions, one of the leading engine manufacturers, estimates that over 30% of newbuild orders in 2023 were for dual-fuel engines, a clear sign that the industry is hedging its bets.
“Dual-fuel is the smart play right now,” says Dr. Uwe Lauber, CEO of MAN Energy Solutions. “It gives shipowners the option to run on LNG where it makes sense, while still having a fallback for routes where LNG isn’t available. And as the technology matures, we’re seeing these engines become more efficient and reliable.”
For operators still committed to HFO, scrubbers have become a lifeline. These systems, which wash exhaust gases with seawater or a chemical solution, can remove up to 98% of sulfur oxides, allowing ships to keep burning HFO while complying with IMO regulations. Scrubbers aren’t cheap—installing one can cost $2-5 million per ship—but for many operators, they’re a cheaper alternative to switching fuels.
“Scrubbers were the industry’s Band-Aid,” says John Hatley, Vice President of Marine Solutions at Wärtsilä, a leading scrubber manufacturer. “They bought us time, but they’re not a long-term solution. The IMO’s 2030 and 2050 decarbonization targets are looming, and scrubbers alone won’t get us there.”
Indeed, the IMO’s 2030 goal—a 40% reduction in carbon intensity from 2008 levels—is just the first milestone. By 2050, the organization aims to cut total greenhouse gas emissions from shipping by at least 50%. For an industry that still relies on fossil fuels for 99% of its energy, that’s a daunting challenge. LNG may be a step in the right direction, but it’s not the finish line.
The Road Ahead: Beyond LNG
So what comes next? If LNG is the bridge fuel, what’s on the other side? The short answer: no one knows for sure. But the maritime industry is placing bets on a few key technologies.
- Ammonia: A zero-carbon fuel that can be burned in modified internal combustion engines. It’s energy-dense and doesn’t require cryogenic storage like hydrogen, but it’s toxic and corrosive, raising safety concerns.
- Hydrogen: The ultimate clean fuel, producing only water when burned. But hydrogen is extremely difficult to store and transport, requiring either high-pressure tanks or cryogenic temperatures. For now, it’s only viable for short-sea shipping.
- Methanol: A liquid fuel that can be produced from renewable sources. It’s easier to handle than ammonia or hydrogen but has lower energy density, meaning ships would need larger fuel tanks.
- Battery-electric: For short voyages, batteries are already a reality. Norway’s Yara Birkeland, the world’s first fully electric autonomous container ship, proves that zero-emission shipping is possible—at least for small, local routes.
For deep-sea car carriers, though, the path forward is less clear. “We’re in a period of experimentation,” says Mikael Karlsson of UECC. “LNG is our focus today, but we’re already looking at what comes next. Ammonia seems promising, but the infrastructure isn’t there yet. Hydrogen is exciting, but the storage challenges are enormous. It’s going to take time—and a lot of collaboration—to figure this out.”
One thing is certain: the days of HFO are numbered. Whether the industry transitions to LNG, ammonia, hydrogen, or something else entirely, the shift is underway. And for the crews, engineers, and operators who keep these ships running, that means one thing: adapt or get left behind.
As Captain Bergström puts it: “Twenty years ago, no one cared what fuel a ship burned. Today, it’s all anyone talks about. The industry is changing, and if you’re not part of that change, you’re going to be the one stuck at the dock.”