The Two-Stroke Wars
(Originally printed in Boating World Magazine in 1998.)

On August 31, 1996, the U.S. Environmental Protection Agency (EPA) published its Final Rule regarding emissions standards for marine engines. The goal was simple and noble. The EPA wrote: "Working cooperatively with the marine industry, the Environmental Protection Agency (EPA) is issuing regulations that will bring forth a new generation of marine engines featuring cleaner technology and providing better engine performance to boat owners. Controlling exhaust emission from new gasoline spark-ignition (SI) marine engines will result in an unprecedented 75% reduction in hydrocarbon (HC) emissions from these engines by the year 2025." [1]

And there the troubles began.

While the Rule might seem unassailable on the surface - after all, nobody supports pollution, right? - it has been the flash point for some of the most highly charged boating arguments in recent memory. In the not-quite-two years since the EPA's marine emissions standards were published, both environmentalists and marine industrialists have found plenty to complain about, with charges and counter-charges flying almost weekly. Caught in the middle, boaters have found themselves wondering if they're evil incarnate or innocent victims in this drama.

It's a legitimate concern. Press releases and public comments from environmental groups such as the Bluewater Network, a project of the Earth Island Institute and the most high-profile critic of the EPA regulations and marine pollution, routinely make statements such as, "The two-stroke outboard motor, found on most boats and PWC, is America's largest source of toxic hydrocarbon pollution." [2] Claims that are answered by calls to arms like, "Your help is needed to hold back the forces that are trying to ban boats in California!" [3] It's no wonder boaters are confused and more than a little unsettled by this issue.

"It's extremely confusing for everybody," agrees Tony Esposito of Mercury Marine, "especially for people who just want to go out skiing for a couple of days, or catch a few fish with the kids."


There are three primary factions in the marine pollution debate: Environmentalists, represented by the Bluewater Network; the marine industry, represented by the National Marine Manufacturers Association and various industry representatives; and the EPA. Of the three, the Bluewater Network is probably the least familiar to the "average boater."

So just who is the Bluewater Network? "Bluewater Network is a coalition of sailors and boaters, divers, sportfishers, scientists, and clean water advocates working to reduce the environmental impacts of recreational boating. Established in June, 1996, as a project of Earth Island Institute, Bluewater Network is ... the only national organization focused on reducing pollution and environmental impacts from motorized watercraft." [4] That focus is the driving force behind Bluewater's Two-Stroke Engine Campaign: "Bluewater Network's immediate goal is to eradicate the unprecedented petrochemical discharge into aquatic ecosystems from marine two-strokes and personal watercraft. Bluewater will achieve this goal by pursuing the following activities: 1) Educate marine users and the general public; 2) Sponsor the nation's first outboard motor retirement program; 3) Strengthen regulations at the EPA; 4) Provide information on marine motor pollution; and 5) Legally pressure manufacturers to replace two-stroke with four-stroke technology." [5]

The "legal pressure" has been steady. Since Bluewater's inception, the organization has filed high-profile lawsuits against the EPA (in the U.S. Court of Appeals), alleging that the EPA's Final Rule should have called for a 95% reduction in emissions (instead of 75%); and against marine engine manufacturers, claiming the manufacturers have violated California's Proposition 65, the Safe Drinking Water Act.

While the EPA is refraining from comment, the marine industry isn't taking the lawsuits lying down. "We are, in this industry, outdoorspeople, conservationists, and environmentalists," emphasizes Mercury's Esposito. "Eighty percent of the two-strokes we sell are used for some fishing. We have an extremely high stake in making sure that our waters remain healthy so people can continue to fish so they'll continue to buy engines. So we're involved with a number of environmental and conservation groups and work very closely with them. Not only is it the right thing to do, but we have a vested interest in it from a financial point of view. Good waterways ensure that people are out there boating and fishing and skiing and all of the other things they use a boat to do."

Esposito adds, "Exhaust from an outboard doesn't effect water quality. When those hydrocarbons hit the water, the unburned fuel is what it is, virtually all of it evaporates almost immediately, and the balance of it evaporates in like the next 10 minutes. So you see this little sheen out there on the water, but the hydrocarbons evaporate into the air, not into the water, and that's why it's an air-quality issue, not a water-quality issue. The one EPA study that was done bears this out. No impact on wildlife, no impact on plant life. It's strictly an air-quality issue."

The distinction Esposito makes between air-quality and water-quality is echoed by Bill Rush of OMC, who points out, "The hydrocarbon emissions from outboard motors and PWC are really categorized into three categories - hydrocarbons, carbon monoxide, and NOx. Most people's attention has been focused on hydrocarbons. Hydrocarbons are also a class of chemicals called volatile organic compounds (VOCs). By their very nature, VOCs evaporate from wherever they are, on the ground or in the water, and go into the air. That's why the EPA recognized this is an air emissions issue. All the evidence still points to that and there's nothing to cause us to think any differently."

Not surprisingly, Dr. Russell Long, PhD, the founder of the Bluewater Network, disagrees. "Over one billion pounds of hydrocarbons will be discharged - emitted - through recreational boating in 1998, according to the EPA," he says. "That's their estimate. And at least 95% of it will be from two-stroke engines, so basically all of it. That's equivalent to 15 Exxon Valdez spills, in terms of the sheer volume. These are emissions into the water from two-stroke engines. The general claim is that it all evaporates, but even the EPA didn't say that. The EPA said that up to 50% of that volume evaporates, while the other 50% remains water-bound for significant periods. That portion of the emissions is the most toxic. It tends to be the heavier elements, even the three, four, and five-ring benzenes, and the PAHs (polycyclic aromatic hydrocarbons), which are the result of burning oil, the combustion by-product of burning oil."

The EPA did consider water quality when formulating its emission standards, writing, "EPA acknowledged in the proposal that marine engine emissions impact water quality, but the Agency presented reasons why the proposal did not contain provisions specifically addressing the water quality impacts of marine emissions." [6] The EPA went on to say, "While Section 213 of the Clean Air Act does not preclude the Agency from considering and addressing water quality impacts, the primary focus of this rulemaking is the effects of gasoline spark-ignited engines on air quality. The Agency believes this regulation will decrease the water quality impact from marine engine emissions through the reductions in exhaust emissions required by this regulation for the reasons set forth in the proposal; however, the sparse data currently available makes it clear that more information is needed to understand the impact from marine gasoline SI engine exhaust emissions on water quality." [7]

That position is supported by independent experts who claim 80% of two-stroke emissions wind up in the air, such as Bill Welch, principal development engineer at the Center for Environmental Research and Technology at the University of California-Riverside, who told the Wall Street Journal, "Most of the compounds that come out of the exhaust are hydrophobic - that is, they bubble up out of the water and go into the air." [8]


The question of whether marine emissions are an air-quality or water-quality concern are crucial to Bluewater's lawsuits against the marine manufacturers. The manufacturers, needless to say, are willing to concede that two-stroke emissions are an air-quality issue, as defined by the EPA, instead of a water-quality problem because that would knock the legs out from under Bluewater's claim that the manufacturers are violating California's Safe Drinking Water Act. Bluewater, on the other hand, staunchly argues that water quality is the main issue. Bluewater quotes several studies to support their position (see sidebar), indicating that emissions into the water from marine engines is potentially dangerous to fish, plants, and humans.

OMC's Rush takes issue with the Bluewater studies, pointing out, "There has never been a problem, any sort of a known damage to a fish population or any sort of a need to shut down lakes, etc., associated with the use of our products on lakes. Given that very good history, what we need to recognize is that the new products are going to make things a lot better, and in the near term. History has not presented us with any credible evidence that there's any sort of a problem."

Why is the air-quality vs. water-quality aspect of the debate so important, aside from the obvious financial issues arising from the lawsuits? Possibly because framing the debate over water quality is a way of focusing on a particularly vulnerable target, according to Mark Denny of the International Jet Sports Boating Association (IJSBA), who told the Wall Street Journal that regulators, "aren't able to get where they want to go with car manufacturers, and they hit a pretty solid political brink wall with stationary sources (factories, etc.). So they're going to go after weaker industries like ours." [9]

There's reason to believe Denny may be right. Looking at the question of air quality, the EPA claims that nonroad sources as a whole contribute 10% to average hydrocarbon inventories. Of that 10%, recreational marine engines are responsible for 30% of the total (other small SI engines, such as lawn mowers, are responsible for 50%). This means recreational marine engines are responsible for a mere 3% of all hydrocarbon emissions. As the EPA emission standards go into effect, that will drop to less than 1%.


Despite the often incendiary rhetoric, both the environmentalists and the marine industry agree that the issue of marine emissions can be, and is being remedied. The sticking point - and there had to be one - is in how and how fast.

The Bluewater Network points to four-stroke technology as the best option. "A carbureted two-stroke engine emits more than 150 gram of hydrocarbons per kilowatt-hour," Long says. "A direct-injection two-stroke emits 20-40 grams per kilowatt-hour. But a four-stroke emits less than four grams per kilowatt hour. A lot of problems are difficult to resolve because there's no clear answer. But this is one where there is an answer, and it's clear. We have technologies today to reduce pollution by over 95%. Let's use them."

Mercury's Esposito argues, "It sounds great - we've got four-stroke technology, let's switch to that. The economic reality is a little bit different. Plus there are some trade-offs between two-stroke and four-stroke technology. Four-stroke is heavier. It doesn't accelerate in quite the same way. There are things people like about their two-stroke outboards, the performance and the acceleration and that kind of thing, that they can't get in a four-stroke right now."

Not to mention the fact that according to the NMMA, boaters currently own more than 13 million outboard motors. Using a Honda 90-hp four-stroke (MSRP - $9455) and an Evinrude 90-hp FICHT two-stroke (MSRP - $6995) for examples, the potential cost to the boating public of upgrading to four-stroke outboards instead of low-emission two-strokes would be nearly $32 billion. While it's a sure thing that the engine manufacturers would love to get their pieces of that enormous pie, it's highly doubtful that anywhere near that many motors would actually be sold. More realistically, the vast majority of recreational boaters would simply give up and find other ways to spend their leisure time. And that's the worst possible solution to the problem.


Fortunately, there's virtually no likelihood that anyone will ever be forced to buy a new motor unless he really wants or needs one. The EPA spells this out clearly when it says, "Boat owners are in no way responsible for making modifications to their current engines to meet the standards or subject to any penalties as a result of this rule" [10] As a result, the economic impact on the boating public as a result of the EPA standards will be almost nil, especially when the fact that the new generation of direct-injection two-strokes will deliver dramatically improved fuel economy over carbureted two-strokes, something that will greatly counter the increased cost of the new engines over traditional carbureted motors.

So much for the potential victimization of boaters, at least financially. But what about the cost to the environment? There is no question or debate that carbureted two-stroke is a technology whose time has past. As OMC's Rush says, "Both four-stroke and direct-injection two-stroke are excellent, low-emission technologies, and both are immensely improved over the carbureted two-stroke emission performance. Looking at the averages, the new technology engines are a ten-fold improvement in emissions. The new technologies emit about 1/10 the pollution of their predecessors."

It's important to point out that while much of the debate centers around outboard motors, PWC must not be overlooked. PWC represent a huge portion of the new boating market, and because of their high horsepower:weight ratio, they're perhaps the least likely beneficiaries of improved emissions via four-stroke technology. But even the much-maligned PWC are working hard to clean up their act environmentally, with Polaris recently announcing the use of OMC's FICHT direct-injection technology in their upcoming craft, and similar announcements expected in the near future, according to OMC spokesperson Marlena Cannon.

So while boaters must still do everything they can to further reduce pollution, such as keeping their boats and motors in top operating condition, cautious refueling to eliminate spillage, and investing in the cleanest possible technology when buying a new motor, they can shake off the stigma of being the scourges of the environment. The final word - for the time being - is that there is common ground where everyone on every side of the issue can meet and agree that, in the words of Bluewater's Russell Long, "What we do want to do is reduce pollution as much as possible and get rid of polluting technologies to keep our waters clean and pure for us and our kids."


  • [1] EPA Environmental Fact Sheet EPA420-F-96-012, August 1996.
  • [2] Bluewater Network press release, "America's #1 Source of Toxic Hydrocarbon Marine Pollution."
  • [3] National Marine Manufacturers Association press release, "NMMA Action Alert", February, 1998.
  • [4] Bluewater Network website (
  • [5] ibid.
  • [6] EPA Office of Mobile Sources Air Docket A-92-28, "Control of Air Pollution; Emission Standards for New Gasoline Spark-Ignition Marine Engines," Summary and Analysis of Comments, June 1996.
  • [7] ibid.
  • [8] "State Air Panel Begins to Focus on Jet Skis," by Jess Bravin, The Wall Street Journal (California edition), February 18, 1998.
  • [9] ibid.
  • [10] EPA Environmental Fact Sheet EPA420-F-96-012, August 1996.
    Bonus Section - Seeing Clearly?

    It's been said that there are "lies, damned lies, and statistics," and the issue of marine pollution is a near-perfect case in point. Statistics, seemingly innocent findings, can be made to say almost anything, so it's important to cast a jaded eye on any claim supposedly supported by research.

    In researching this article, I read a number of studies quoted by both environmentalists and the marine industry. While neither side ever said anything even vaguely untrue regarding the studies and their findings, both sides tended to quote only the parts of the studies that served their purposes. And I'll almost certainly be guilty of the same thing.

    My findings were unpleasantly simple. While the EPA Analysis quoted by Mercury Marine attempted to study a real-world situation, Florida's "Lake X", a private Mercury test lake, the study was, in my opinion, fatally flawed due to its age - it was conducted from 1971-1973, rendering it irrelevant today. In other studies, such as the Swiss studies of two- and four-stroke emissions and the Swedish study on the effect of two-stroke emissions on fish, I found the methodology flawed. The studies attempted to extrapolate laboratory-derived results into the real world, something that's virtually impossible due to the number of uncontrollable variables in a real-world environment. While no one can dispute the Swiss findings that carbureted two-strokes emit pollutants into the water, and that pollutants can be correlated to water toxicity, the studies sampled water taken from an 800-liter test tank filled with tap water - not a lake or river where bio-organisms or flow might affect the dilution or evaporation rate. The Swedish studies of two-stroke emissions' toxicity on fish were conducted by injecting fish and fish embryos with diluted emittants - not quite a "real-world" condition. Exhaust is certainly not beneficial to fish, especially young fish, but there must be a better way of determining exactly how detrimental exhaust is.

    Dr. John P. Giesy, PhD, of Michigan State University, made a written statement to the Tahoe Regional Planning Agency, in which he refers to the Swiss and Swedish studies, as well as studies done at Switzerland's Lake Constance, in an attempt to answer the question put to him: "Is it possible that petroleum hydrocarbons released to Lake Tahoe from outboard, two-stroke engines in recreational watercraft could cause toxicity to aquatic organisms and pose a hazard to the aquatic populations of Lake Tahoe?" His answer - yes, it is possible. But, and this is what's usually left out, he qualified his answer by writing, "Because I have not had an opportunity to review all of the available literature and because I have not had an opportunity to view Lake Tahoe and collect my own information, at this time I can only indicate the potential for adverse effects to occur from continued inputs of PH from the use of two-stroke outboard engine in recreational watercraft." He then says, "I agree with the authors of the report entitled: 'Lake Tahoe Motorized Watercraft Impact Analysis' (Feb. 1997), when they state on page 3-9 of that report that, 'The cumulative impact of hydrocarbon emissions on water quality and the aquatic environment cannot be accurately quantified at this time.' I think the possibility of hazard does exist and that further analyses would be necessary to determine that the operation of two-stroke outboard engines is completely safe for the aquatic environment."

    That's almost exactly what the EPA found in "Office of Mobile Sources Air Docket A-92-28, Summary and Analysis of Comments, Control of Air Pollution; Emission Standards for New Gasoline Spark-Ignition Marine Engines," writing: "The Agency believes this regulation will decrease the water quality impact from marine engine emissions through the reductions in exhaust emissions required by this regulation for the reasons set forth in the proposal; however, the sparse data currently available makes it clear that more information is needed to understand the impact from marine gasoline SI engine exhaust emissions on water quality."

    The facts, as I see them? There needs to be more study. Real-world study. Until then, I have to accept the position that while pollution is undeniably a problem that must be addressed, history has not yet borne out dramatically adverse effects on aquatic flora or fauna from the use of any marine engines.

    I'm ready and willing to be proved wrong. Just don't try and do it with statistics.

    Back to the Presidential Library...

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