PROS and CON-verters
The Environmental Protection Agency (EPA) estimates that Americans spend more than 500-million hours pleasureboating each year and says that the emissions from that activity are a major cause of air pollution. So in 1990, Congress ordered the agency to set acceptable emission levels for marine engines as part of the Clean Air Act.
But the road that led to those regulations really began in California where, says the EPA, car and marine emissions are main contributors to air pollution. Anyone who has visited California, especially the southern region, knows that air quality is a major problem and a hot issue there. Of the 50 states, California has both the most cars and the dirtiest air in the nation. That's why in 1967 the state created the California Air Resources Board (CARB). Eight years later the first catalytic converters appeared on cars, mainly to meet increasingly stringent CARB standards, and within a few years they were standard equipment on virtually every production automobile. It wasn't too much later that the EPA and CARB began preparing the country for the move to catalytic converters on non-automotive engines.
That first converter was called a two-way because it attacked two basic kinds of pollutants: carbon-monoxide and hydrocarbons (unburned fuel). In 1976 Volvo introduced the first three-way converter, which is the type in use today on all car engines except diesels. The three-way is so named because it attacks three pollutants: not only the two aforementioned, but oxides of nitrogen as well. It does this using two catalysts. The reduction catalyst uses platinum and rhodium to reduce nitrogen oxides; the oxidation catalyst employs platinum and palladium to burn carbon monoxide and hydrocarbons.
In both stages, oxygen is a crucial component; if there is not enough of it in the exhaust stream, the burn will be incomplete. To ensure that doesn't happen, a catalytic converter needs an oxygen sensor upstream that tells the electronic fuel injection system to adjust the ratio of fuel to air going into the engine. The requirement for such precise and rapid adjustments explains why a catalytic converter works best on an engine with electronic fuel injection.
A lot of heat—upwards of 1,200F— is produced when pollutants burn in a catalytic converter, which is why cars and trucks with them also have heat shields protecting the interior of the vehicle. But while it's a potential hazard, heat is also crucial to the efficiency of the converter. If the unit doesn't get hot enough, the pollutants won't burn completely.
Today catalytic converters have a stellar track record, both in terms of their effectiveness at cleaning up exhaust and in the minimal maintenance required of them. So if they've worked so well on automobiles, why haven't they been installed on boats? The short answer is that the boating industry has been able to fly under the EPA and CARBs' radars. But no more. CARB has created new emission standards that take effect in 2010 and apply to all "off-road" gasoline engines. Recreational watercraft will then have to reduce hydrocarbon and nitrogen-oxide emissions by 70 percent and carbon-monoxide emissions by 20 percent. Given the size of the California market and based on the history of past regulations, it is fair to assume that these standards will eventually become national regulations.
This article originally appeared in the January 2009 issue of Power & Motoryacht magazine.