As the push toward lower-emission fishing vessels gains momentum, alternative diesel fuels– renewable diesel, biodiesel, and other drop-in options– are often framed as a near-term solution.
But there are many obstacles to overcome. After years of covering engine technology and vessel design, National Fisherman boats and gear editor Paul Molyneaux says the transition to alternative fuels looks very different from past shifts, like the move to Tier 2 and Tier 3 engines.
“That transition was mandatory and heavily supported,” Molyneaux said. “There were programs that subsidized it. I don’t see anything like that happening yet with alternative fuels.”
A different kind of transition
Unlike earlier regulatory changes, which came with funding and clear pathways, alternative diesel is emerging in a more uncertain environment.
While Molyneaux noted that many engine manufacturers, such as Cat, MAN, and Cummins, are preparing for alternative fuels– designing marine engines that can be modified or adapted down the line—the supply chain and infrastructure don’t exist yet. “The companies are ahead of the curve,” he said. “They’re getting engines ready so they can run on alternative fuels when the time comes.”
But for fishermen, the question isn’t just whether the technology works. It’s whether it fits into the reality of their operations.
From what Molyneaux has seen, fishermen are aware of alternative fuels– but they’re not rushing to adopt them. “They know about it. They’re thinking about it,” he said. “But they’re not really seeing these fuels at the dock. It seems like if they want the advantages that alternative fuels offer, they may have to take the initiative and go get the fuels, basically create their own supply chain.”
Molyneaux noted that going back to the 1970s a few fishermen, particularly in Louisiana, were collecting used cooking oil from restaurants, carefully filtering it, and burning in their Detroit 71 series engines.
Incremental gains over big leaps
Those experiments with cooking align with how many fishermen approach change: adopt what works, when it makes sense, without overhauling the entire system. They also provide a platform for the idea of alternative fuels and open the door to other options, such as methane, hydrogen and LPG.
One of the key questions around alternative diesel is whether existing vessels are ready for it.
The answer, according to Molyneaux, is mixed. “It depends on the engine,” he said. “Some systems can handle alternative fuels more easily than others. The cooking oil, for example, works best in older mechanical engines, not so great with common rail high pressure fuel injection.”
But it’s not always as simple as just switching fuels. In some cases, different fuel properties may require adjustments in storage, handling, or engine setup. That added complexity can be a deterrent, particularly for smaller operators.
Infrastructure remains the biggest hurdle
If there’s one concern that comes up consistently, it’s infrastructure. Fuel availability– especially in remote ports– is a major question mark.
“Availability is huge,” Molyneaux said. “You can’t run a boat on something you can’t reliably get.” For fleets operating in places like Alaska or along rural coastlines, the idea of consistent access to alternative fuels– or the infrastructure needed to support them– can feel far off.
Complicating matters further is the uncertainty around costs and funding.
Molyneaux noted that shifts in federal policy and the availability of subsidies can have a direct impact on fishermen’s willingness to participate in new programs.
“If someone comes to you with a grant and says, ‘We’ll help you make these changes,’ you need to know that money is actually going to be there,” he said. Without that certainty, the risk falls squarely on the vessel owner.
“That confidence matters,” he added. “Otherwise, you’re asking fishermen to take on a lot of risk.”
So where do alternative fuels fit in the bigger picture? For now, it may serve as a bridge– an incremental step toward lower emissions without requiring a complete overhaul of vessel systems. But whether it has long-term staying power remains an open question.
“Fishermen building new or looking to repower might ask, ‘Can this engine be converted to other fuels later?’” Molyneaux said. “That’s where the thinking is– keeping options open for what may be coming. Our domestic production is high, but much of the crude refined for diesel comes from overseas, is high in sulfur, and vulnerable to price fluctuations in the global market.”
For now, the pace of change is being set not by policy or technology–but by the realities of commercial fishing. “For the most part, these guys are practical,” Molyneaux said. “They’ll look at something, and if it works for them, they’ll adopt it. But it has to make sense on their boat, in their fishery, right now.”
Until alternative fuels meet that standard across the board, adoption is likely to remain gradual–driven by opportunity, not obligation.
