What Do Those Star Ratings Mean on Boat Engines?

What does the CARB star rating mean and how does it relate to EPA regulations?

CARB emission standards are similar to EPA in that they regulate certain aspects of engine emissions that affect air quality. CARB standards, however, are stricter than Environmental Protection Agency (EPA) standards because they call for an accelerated emissions reduction schedule in California. For example, the 2001 CARB one-star standard is equivalent to the 2006 EPA standard. Most outboard manufacturers choose to certify engines to the CARB two-star and three-star levels because they are well below the EPA standards. EPA “credits” can be earned by manufacturers’ engines that are certified below the EPA certification levels, and those credits can be used to offset negative credits imposed on engines that are certified above the EPA standards. The illustration below explains in further detail what each of the CARB star ratings mean.

  CARB’S One Star label identifies engines that meet CARB’s 2001 exhaust emission standards. Engines meeting these standards produce 75% fewer emissions than conventional carbureted two-stroke engines. These engines are equivalent to the US EPA’s 2006 standards for marine engines.
  The Two Star label identifies engines that meet CARB’s 2004 exhaust emission standards. Engines meeting these standards produce 20% fewer emissions than One Star (Low Emission) engines.
  The Three Star label identifies engines that meet CARB’s 2008 exhaust emission standards. Engines meeting these standards produce 65% fewer emissions than One Star (Low Emission) engines.

Let seabuddy add to this Mercury Marine statement…

There are now 4 star and five star ratings for even cleaner engines since 2008. I have not yet seen a 5 star engine in any boat.

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