Next-Generation Eco-Friendly Marine Fuel Sources

The benefits of the technology are less pollution, fewer greenhouse-gas emissions, and cleaner seas and skies. Karandaev/Adobe.Stock

I will never forget the first time I encountered a boat running on biodiesel. As we walked down a marina crowded with sport-fishers, engines warming up in preparation for a day of fishing on the Gulf Stream, the unmistakable scent of fresh french fries hit me right in the nostrils. I asked the captain about it that afternoon when we returned to the dock. He explained they were using a (then) new alternative fuel called biodiesel, which was a blend of conventional diesel and recycled vegetable oils, including those from fast-food restaurants.

Flash ahead more than a decade, and the use of alternative fuel sources has become a hot topic in the marine industry and beyond, for a number of reasons. By definition, alternative fuels are environmentally friendly, cost-effective and renewable. The benefits of the technology are less pollution, fewer greenhouse-gas emissions, and cleaner seas and skies.

From a report titled “Pathways to Propulsion Decarbonization for the Recreational Marine Industry”, which was commissioned by the International Council of Marine Industry Associations, recreational boats account for less than one-tenth of 1 percent of global greenhouse-gas emissions; however, it is clearly an industry that is deeply invested in helping to preserve the natural resources it depends upon. To that end, the stakeholders have joined to search for ways to further reduce the negative impacts of conventional fossil fuels as we collectively look to the future. 

The 171-foot Special One, was designed to run on HVO100, a fossil-free hydrotreated vegetable oil, which reduces carbon dioxide emissions by more than 90 percent compared with standard diesel. Courtesy Royal Huisman Two Paths to the Future

There are two apparent pathways to long-term, greener fueling solutions: The first involves sustainable conventional marine fuels, and the other relies on innovative new fuel sources such as hydrogen.

According to the National Marine Manufacturers Association, sustainable marine fuels are expected to be the most suitable source of energy for at least the next decade. The good news is that these fuels are readily compatible with the 30 million or so recreational vessels already in use around our big blue planet. (It’s blue because of the oceans, remember?) These are termed drop-in fuels because minimal or even no engine modifications are required, and there are readily available alternatives for both gasoline and diesel engines. This could potentially mean wide-scale reductions in carbon emission with widespread adoption.

One of the drawbacks to alternative fuels on the marine side lies with that last phrase: widespread adoption. The other key factor is price. Most marinas typically don’t have the room to expand their fuel footprint to offer alternatives, and tend to avoid ones that are cost-prohibitive for the customer.

In July 2024, the NMMA and several partners—including Suzuki Marine and Hyperfuels—launched a pilot program for sustainable marine fuels at St. Andrews Marina in the Florida Panhandle, which could serve as a blueprint for future projects. The program replaces the marina’s conventional gasoline with a 93-octane, ethanol-free premium gasoline called Purfuel, produced by a Texas-based company called Hyperfuels. Purfuel is a non-alcohol high-octane blend with renewable content, which is developed from the leftover starch from corn used for producing high-protein animal feeds; the starch is separated from the kernel to create energy-dense liquids. It is designed specifically for the ethanol-free gasoline market, and it also reduces carbon dioxide emissions by up to 30 percent more than comparable fuel containing 10 percent ethanol. And although long-term testing is still underway, early reports show that performance and fuel economy are at least as good as—if not slightly better than—with conventional petroleum gasoline.

And yes, ethanol and its blends are alternative fuels in their own right—comprising roughly 98 percent of all gasoline sold in the United States in 2023—but they can do damage to a boat’s fuel systems. So having an alternative free of ethanol alleviates that concern.

But what about the price? As of this writing, the Hyperfuels product was selling at $4.77 per gallon, while standard non-ethanol gasoline was running at $5.09 a gallon. And while this was just one example, the keys to these drop-in replacement fuels will continue to be price and availability, given that head-to-head performance appears similar.

At the other end of the spectrum, owners and builders of the world’s largest sport-fisher, the 171-foot Special One, announced that the vessel was designed to run on HVO100, a fossil-free hydrotreated vegetable oil, which reduces carbon dioxide emissions by more than 90 percent compared with standard diesel. HVO is produced from food-industry waste and is 100 percent renewable and traceable.

“We applied our most radical naval architecture to date on this hull, resulting in lower resistance and, consequently, reduced fuel consumption,” says Bart Bouwhuis, co-creative director of Vripack, the firm responsible for the naval architecture. “However, we were also acutely aware that the two V-20 MAN engines and twin Zenoro 180 kW generators will always burn a substantial amount of fuel. This fossil-free fuel is a highly welcome alternative.” Along with reducing emissions, Bouwhuis also says that the engine components, including filters and injectors, stay cleaner and require less maintenance using the HVO100 fuel. 

In early May, Dutch shipyard Feadship unveiled the first fuel-cell-powered superyacht, known as Project 821. Courtesy Feadship Making the Switch

Hydrotreated vegetable oil’s similarity to so-called fossil diesel fuel means that it’s a true drop-in replacement, requiring no modifications to the engine or the fuel system. It can also be mixed with conventional diesel without harmful effects. For those reasons and more, German engine manufacturer MTU has approved it for use in its popular Series 2000 and Series 4000 marine engines. “HVO sustainable diesel can be used in any of our engines today,” says Denise Kurtulus, vice president of Global Marine at Rolls-Royce Power Systems, MTU’s parent company. While Kurtulus sees methanol fuel as the long-term goal for cleaner emissions, she deems HVO as a winning stopover in the energy transition. “We can’t just jump into [using methanol], but one thing we can do now is start to use HVO. The technology is there, and using HVO reduces carbon dioxide emissions by 90 percent.” Feadship and Azimut-Benetti have designed yachts to run exclusively on the new biofuel. Feadship’s 84-meter Obsidian, launched in 2023, was its first to use HVO.

The Defining Alternate Fuels

Biodiesel: A clean-burning fuel made from vegetable oils, animal fats or recycled restaurant grease. It has similar physical properties to petroleum diesel and can be blended with it.

There are three grades of biodiesel: B5 is a blend of 5 percent biodiesel and 95 percent petroleum diesel, which is usually less expensive than other blends. B20 is 20 percent biodiesel, which is usually more expensive than B5 but less expensive than pure biodiesel, while B99/B100 is known as pure or neat biodiesel, which is usually the most expensive of the three blends.

Ethanol: A renewable fuel made from corn and other plant-based materials. More than 98 percent of gasoline in the US contains some ethanol, usually in a 10-percent-ethanol/90-percent-gasoline blend called E10. Ethanol can also be used in its pure form, which is aptly labeled “E100.”

Propane: Also called liquefied petroleum gas, propane is a nontoxic, colorless gas that is normally compressed and stored as a liquid. Conversion kits are available for gasoline engines to run on propane.

Other sustainable-fuel examples include methanol, which is a versatile, affordable replacement for gasoline-based fuels. Biobutanol—made from biomass feedstocks—is another alternative, as is electricity produced from solar panels.

Hydrated Vegetable Oil is a renewable diesel fuel made from vegetable oil and hydrogen. Supamas/Adobe.Stock Hydrogen Equation

In 1839, Sir William Grove created the first fuel cell—combining hydrogen and oxygen to generate electricity—with water as the only byproduct. It came to be known as Grove’s gas battery. The ability to power fuel cells without generating nasty byproducts such as carbon dioxide and other pollutants has made hydrogen the center of attention for quite a while in the nautical realm, with several high-profile projects now hitting the water in real time.

In early May, Dutch shipyard Feadship unveiled the first fuel-cell-powered superyacht, known as Project 821. At just under 120 meters in length, it is the largest noncommercial vessel to run on hydrogen, but the challenges remain tall, and include basically rewriting the regulatory rule book to include hydrogen storage and safety at all levels (safely storing hydrogen on a vessel requires a double-walled cryogenic storage tank in a dedicated space). Hydrogen also requires approximately 10 times the room compared with standard diesel fuel. And while the builder noted that even a vessel of this size cannot carry enough liquid hydrogen for transatlantic crossings, it can greatly minimize the yacht’s hotel load emissions, which comprise 70 to 78 percent of the vessel’s total energy usage per year.

The technology offers clear benefits: better air quality, cleaner seas, and no significant drop in performance. Additional advantages include lower maintenance and fuel costs, especially as biofuels and alternatives such as hydrogen become more accessible to boaters. It’s a win-win for us all, and especially our big blue marble.

American Magic is a 33-foot carbon-fiber hydrofoiling catamaran powered by two hydrogen fuel cells and three 63 kWh batteries. Courtesy Bluegame Chasing Zero Emissions

Those watching this year’s America’s Cup may have noticed some rather unusual chase boats shadowing the fleet. The Cup defenders at Team New Zealand included a stringent set of parameters for the tenders used by each team: The vessels had to be capable of maintaining 30 knots cruising speed over a minimum of 150 nautical miles, while also achieving a maximum speed of 50 knots for more than one hour. They also had to be hydrogen-powered.

The New York Yacht Club team turned to Bluegame, an Italian shipyard that is part of the Sanlorenzo group, to build their chase boat. The result was American Magic, a 33-foot carbon-fiber hydrofoiling catamaran powered by two hydrogen fuel cells and three 63 kWh batteries. The tender shares more with Formula One racers or sixth-generation fighter aircraft than the average runabout at your local marina, with the ability to operate in standard cruising mode or fly on foils at high speeds, while producing no emissions and no noise other than the sound of the propellers.

Bio-Fuels

Hydrated Vegetable Oil

• HVO is a renewable diesel fuel made from vegetable oil and hydrogen.
• Reduces carbon dioxide emissions by more than 90 percent compared with standard diesel fuel.
• It’s 100 percent renewable and traceable.

Ethanol-Free

• Fuels made without ethanol typically have a longer shelf life.
• They also reduce damage to fuel systems caused by ethanol-based fuels.
• $5.09 Ethanol-free gasoline cost per gallon

Purfuel

• Developed from the leftover starch from corn used for producing high-protein animal feeds.
• Purfuel is made with renewable content.
• Reduces carbon dioxide emissions by up to 30 percent more than comparable fuel containing 10 percent ethanol.
• $4.77 Purfuel cost per gallon

Biodiesel

• Clean-burning fuel made from vegetable oils, animal fats or recycled restaurant grease.
• Can be blended with petroleum diesel.

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