Mark Rothfield | VOLUME 24, ISSUE 4

More input in technology has resulted in less output in emissions, as outboard engine manufacturers strive to create leaner, greener and meaner powerplants.

D’oh! I clearly remember the first time I tried to start a four-stroke outboard that was already quietly going about its business on the transom. As the starter motor and boat owner whined in protest, it was more like an epiphany than just another “senior moment”.

It was a decade ago and, to someone long raised on a diet of cantankerous, rattly two-strokes, one erroneous turning of a key also signalled a turning point for the trailerboat industry.

Life with outboards would never be the same again, for a new level of excitement and user-friendliness had been ignited. No smoking, no flatulence or fussing at start-up, less vibration and so little noise at idle you weren’t to know the damn things were running.

We had the Americans to thank – not so much for the technological leap, but the legislation which begat it. When America sneezes, the financial world gets a cold; when an outboard wheezes, we get environmental laws.

In 1998, the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) dipped their toes in the sparkling alpine waters of Lake Tahoe and solemnly declared that conventional two-stroke outboards would be banned. Federally, they nominated 2006 as the cut-off year for manufacturers to reach stringent new emission goals.

Hewn by glaciers two million years ago and now sleeping amongst verdant valleys, Tahoe is stunningly beautiful, extraordinarily deep, and relatively sensitive, due to a lack of natural flushing. Equally pristine and delicate waterways exist all over the world, of course, so it was inevitable that a line would be drawn on a sandy shoreline somewhere.

At no stage was Australia implicated in the marine legislation, but the US market was too big to ignore and Europe was set to follow suit.

Debate raged as to whether it was fair to target outboards among the two-stroke brigade, since far more motorcycles, lawn mowers, chainsaws and the like littered the planet. But the car industry had been copping the EPA’s wrath for years, plus there was a compelling argument that boats required substantial power to lift onto the plane.


Even with the 2006 emission standards applied, one hour of operation of a “green” outboard still produced the same pollution as 50 cars run at a similar speed. Older-style outboards were 10 times worse than conforming engines.

Among the emissions were volatile organic compounds (hydrocarbons to their friends), oxides of nitrogen, carbon monoxide and a range of water and air toxins such as benzene.

Petrol-driven contrivances had existed since the turn of the century. The American Motor Co of New York produced a motor called the “American” in 1896, which was rated at 2hp, ran at 400 to 600rpm and propelled a rowboat at up to eight miles an hour.

In 1908, old Ole Evinrude was rowing to get ice-cream for his fiancée, Bess, when it occurred to him that a detachable gasoline motor clamped to the transom was the way of the future, if only to stop the ice-cream melting.

His first effort was a 1.5hp donk that Bess reckoned looked like a coffee grinder. She came up with the slogan “Throw the Oars Away!”, while Ole continued with his refinements. In 1911 he earned a patent and the days of rowing boats were numbered.

Ninety years later, the days of two-strokes were seemingly numbered as suddenly no carburetted two-stroke complied with the CARB regs.

The fault lay in their inability to completely separate the inlet gases from the exhaust gases – with the exhaust and intake ports being opened simultaneously at the bottom of the piston stroke, a portion of the fuel/air went directly out, unburned, through the exhaust port.

Up to 30 per cent of the fuel was being wasted and, what’s more, oil was being added to the petrol for lubrication. It was a vicious cycle that had to be broken.

Realising it would take time to solve the design challenge, authorities set incremental targets that aimed for 10 per cent improvements annually, as well as allowing a fleet average across the manufacturer’s horsepower spectrum.


The EPA’s 2006 standards identified engines that produced 75 per cent fewer emissions than conventional two-stroke engines, but the Californians moved the goalposts forward to 2001. It was designated with a One-Star label.

Two-star engines met CARB’s 2004 standards by producing 20 per cent less emissions than One-Star engines. CARB 2008 carried a Three-Star label, with engines producing 65 per cent fewer emissions than One-Star engines.

There’s also a Four-Star rating for four-strokes, which two-strokes aren’t obliged to meet.

Subsequently, Honda and Suzuki decided that a greener future lay with four-strokes. Certainly, it was easier and cheaper to make them comply, although in those days the automotive-based four-strokes were heavy, complex and lacklustre in mid-range response.

With a power stroke every two engine cycles, as opposed to every four cycles for four-strokes, the two-stroke engine has power aplenty.

Enter “direct injection” for two-strokes, which brought air – and air alone – from the crankcase, with fuel not being injected until the piston rose and all ports were closed.


Opinions were divided on how best to force-feed the combustion. OMC, the manufacturers of Evinrude/Johnson, turned to Ficht injection; Mercury/Mariner chose Orbital technology for the OptiMax injection system, while Yamaha opted for HPDI (High Pressure Direct Injection).

The German-engineered Ficht system was unique in that it didn’t require a high-pressure pump to inject into a closed combustion chamber. Rather, it had an electric solenoid pump for every piston, each capable of producing sufficient pressure.

An enamoured OMC invested heavily, but was plagued by initial warranty issues. Ficht RAM came out in 2000, with fewer parts and higher voltage, but OMC was soon beset by financial problems.

In December 2000 it declared bankruptcy and a year later was bought by BRP, of Sea-Doo fame. Since 2003, Evinrude has been using the simpler, more reliable E-TEC system and has been recognised with the 2005 EPA Clean Air Excellence Award.

E-TEC can inject fuel extremely quickly – with each quarter-turn of the crank – so the burn rate and efficiency is exceptional.

Mercury Marine’s Orbital-based system injects a mixture of finely-atomised fuel and compressed air into the chamber. A three-cylinder, 1.2lt Orbital DI two-stroke had similar power to a four-cylinder, 1.6lt four-stroke, but was smaller, lighter, used less fuel and had lower emissions.

There were fewer reliability issues than Ficht MkI, though the same couldn’t be said for the so-called Smart Gauges that occasionally infuriated owners. Direct injection can’t happen without advanced electronics, which meant introducing computers to the marine environment.

Seeking a long-term four-stroke engine platform, Mercury released the Verado series in 2004. Developed in the United States over five years at a reputed cost of US$100m, this was the world’s first supercharged outboard.

The merry men of Mercury called in Lotus and Cosworth to extract maximum performance from the inter-cooled, 2.6lt inline six. In 2007, a 300hp engine was introduced and there’s now a four-cylinder version.

While the big two slugged it out, Yamaha kept its cards close to its chest and a foot in both camps, if you’ll excuse the mixed metaphors. In 1998, it released the four-stroke, four-cylinder F100A before unveiling a 200hp two-stroke V6 HPDI in 1999.

The HPDI differed from the Ficht/E-TEC and Orbital systems by using a separate, belt-driven fuel pump to mechanically generate the necessary pressure. Meanwhile, EFI was employed on the new 115hp four-stroke in 2001, and in 2007 the industry’s first V8, 5.3lt, four-stroke 350hp giant was unleashed.

Honda Marine stayed faithful to four-strokes and its current production models all meet the standards set forth by CARB 2008.

Next year, the EPA 2010 standards will be applied US-wide, essentially adopting CARB 2008 and adding some evaporative emissions for fuel lines and so on. Henceforth, changes are likely to be evolutionary, not revolutionary, because there has been more change in the past 10 years than the preceding 90.

The current challenge for two-stroke designers is to make the technology economically viable in smaller motors, which are not only price sensitive, but have a smaller differential in fuel usage.

As with carbon credits, there are “averaging, banking and trading” options for outboard companies. So the incentive remains to develop newer and greener motors into the future.


The voluntary Australian outboard engine labelling scheme follows the lead of the USA legislation by focussing on two main pollutant groups. Its aim is to inform buyers of the level of harmful emissions produced by any given engine. Engines are typically labelled to signify their individual star rating.

Hydrocarbons (HC) are unburnt and partially burnt fuels. As well as partially burnt oil and fuel emitted through the exhaust, there is a very long list of complex chemicals that are blamed for an even longer list of human, animal and plant diseases.

The star rating system is as follows:

• Zero Star: High emission (250g/kw/hr) – many carburetted two-stroke engines

• One Star: Low emission – most traditional two-stroke engines, especially EFI

• Two Star: Very low emission – most two-stroke direct injection and a few four-stroke engines

• Three Star: Ultra low emission – some two-stroke direct injection and most four-stroke engines