There’s been a lot of talk about the electrification of boating in recent years, with a range of outboard manufacturers introducing new battery-powered electric motors to compete against established internal combustion engines. Proponents of electric outboards point to their lack of greenhouse gas emissions as being better for the environment.
Critics argue that limitations in battery technology restrict electric outboards to brief run times before they need to go back on the charger, while their expensive lithium-ion battery packs also represent a substantial environmental impact in their manufacture and disposal.
With the discussion weaving back and forth, and tending more toward rhetoric than hard data, it’s hard to know what to believe.
At least, that was the case. But groundbreaking new data presented at the METSTRADE boat industry trade conference in November 2024 suggests that internal combustion engines may not be quite the villains they’ve been portrayed as and could in fact represent the cleanest option for boaties looking to minimise their carbon footprint.
A newly-published research paper commissioned by the International Council of Marine Industry Associations (ICOMIA) compares different propulsion technologies in terms of full-life environmental impact. The new data further identifies the tipping point of each technology, where its use truly begins to reduce carbon emissions.
Titled Propelling Our Future, the study was conducted for ICOMIA by UK-based research firm Ricardo Group. It conducted full cradle-to-grave life cycle analysis studies on five different propulsion types as applied to nine different types of boats, for 45 full data sets in all – making it by far the most comprehensive research on the subject to date. Propulsion options that were studied include traditional internal combustion engines burning petrol or diesel, internal combustion engines burning sustainable biofuels like hydrogenated vegetable oil (HVO), battery-powered electric, hybrid electric, and pure hydrogen. Boat types studied include RIBs, bowriders, personal watercraft, cruisers, sailboats, aluminium fishing boats, pontoon boats, inland waterway commercial vessels and motor yachts.
And the winner?
“We looked at nine different boat types and five different propulsion types, which meant that we did 45 full cradle-to-grave life cycle analysis studies to measure the full impact of different propulsion platforms using existing internal combustion engines burning petrol or diesel as a baseline,” explained ICOMIA president, Darren Vaux. “Switching to internal combustion engines burning sustainable fuels, without question, represents the greatest impact in terms of reducing our carbon footprint.”
In fact existing internal combustion engines burning HVO instead of petrol or diesel were the clear winner in nearly every single boat category studied. The sole exception was personal watercraft, where their comparatively light weight and low mass allowed battery electric propulsion to reign supreme as the cleanest overall option.
The key to the study’s outcomes lies in the simple fact that the highest carbon impact related to boats lies in their manufacture, rather than in their use. Real world monitoring data from engine manufacturers shows that most of us run our boat engines far less than we believe. While we may spend a full day out on the water, in most cases the engine is turned off or only run at idle speed for much of that time. This contrasts significantly with typical usage patterns for cars and trucks, where the engine is typically pulling a load almost all the time. That’s why battery electric systems which can make such a positive ecological impact in cars tend to not achieve the same level of success in boats.
It is that reduced usage which also allows sustainable fuels to make an outsized impact in boats, says Vaux. “We have very firm data in terms of usage, and we have very firm data in terms of vessel average lifespan. Combined, they represent the basis of where the actual tipping points lie, and that data is very clear.”
It turns out the ecological cost of mining rare earth minerals to produce batteries, and the challenge of dealing with their internal chemistry at the end of their life, is a whole lot greater than what was originally believed. Or what we were led to believe, if political objectives are considered. After all, there’s no better photo op for a politician sagging in the polls than opening a new battery plant.
Looking at a mid-sized runabout as an example, the ICOMIA study shows a traditional internal combustion outboard engine using sustainable fuel would deliver an immediate 60% reduction in greenhouse gas emissions over the same vessel and engine burning petrol.
Battery electric systems produce a 100% reduction. But the environmental cost of manufacturing and then disposing of the electric motor and its companion lithium battery at the end of its life greatly exceeds the impact of building and dismantling the internal combustion engine, giving it a higher carbon footprint over its service life.
Where it gets even more interesting is when that immediate environmental impact from switching to sustainable fuels is extrapolated over the full life of a vessel. With ICOMIA identifying an average annual utilisation of 48 hours and a boat and engine lifespan of up to 45 years across all boat types included in the study, fully electric propulsion systems would require boaties to increase their time on the water by an average of 595% every year to achieve the same level of overall environmental impact as running current vessels and engines on sustainable fuels. That increase in usage, says Vaux, is simply not realistic. “If people could spend more time in their boats, they would be doing it already,” he says.
It’s worth noting that those figures reflect an average across all 45 possible power and vessel scenarios. Sailboats tend to skew the average lifespan upwards given how many boats from the 1960s and 70s are still in active use, while commercial vessels skew average hours of use skyward.
Looking at specific categories, the ICOMIA research shows aluminium fishing boats could cut emissions by 60% immediately by burning sustainable fuels instead of petrol or diesel. Large motor yachts with full displacement hulls could achieve a 40% GHG reduction with sustainable fuels, while fuel-thirsty personal watercraft could achieve reductions in the range of 70%. Even sailboats were found to offer emissions reductions of up to 30% by replacing fossil fuels with alternatives like HVO.
So, what about this HVO stuff? Aren’t we just trading one form of oil for another?
Not at all, says Vaux. Unlike fossil fuels, we can grow all the vegetable oil we like, with no need to drill under the sea or frack under people’s drinking water. What’s more, we can start by repurposing the billions of litres of HVO that already go straight into landfills around the world every year after spending just a day or two in a deep-fry vat. The stuff may no longer hold up for preparing food, but it’s still perfectly fine to run in an engine.
Trials in the US bear this out. Suzuki’s US subsidiary has been a vocal proponent of sustainable fuel adoption, collaborating with the National Marine Manufacturers Association, an American boat industry group, to support an HVO pilot project in Florida. The engine builder has now collected more than six months’ worth of data with findings expected later this year. Similarly, Yamaha has also collaborated with efforts to promote the adoption of sustainable fuels in North America and in Europe.
Those pilot projects indicate that most modern engines can burn sustainable fuels like HVO either as-is or with minimal modification required, allowing its immediate implementation. Further, a switch to sustainable fuels allows boaties to reduce emissions while continuing to enjoy their current vessels, eliminating the need to relegate tens of millions of perfectly functional engines to landfill.
Cynics might say that ICOMIA has a vested interested in pushing internal combustion engines since, after all, it is a marine industry trade association. But ICOMIA also represents a range of companies that build battery electric outboards. The reality is, the trade association simply wants to sell more boats and motors around the world, and couldn’t care less if they burn petrol, vegetable oil, run on batteries or are powered by unicorn farts. The fuel they use is irrelevant so long as more people go boating.
Instead of waiting for new batteries to be invented and stretch electric outboard run times from minutes to hours, perhaps we should be looking at ways to cut our emissions right now. The best data available says that using sustainable fuels like HVO can immediately reduce our greenhouse gas emission by up to 60%. Perhaps used deep-fry oil doesn’t have the political photo op cachet as a ribbon cutting at a multi-billion-dollar battery plant, but real-world pilot projects show its use can produce significant, immediate GHG emission reductions. It sounds like a real win-win, and perhaps it is something our elected officials need to examine more closely.
