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Please note: This summary is provided to help you understand the regulations. Consult the references provided for links to the full text of the regulations.

Marine Engine EmissionsEngine Emissions (Marine Engines)

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This page covers regulations that apply to emissions from marine engines of pollutants other than greenhouse gases. See also the TERC articles on greenhouse gas emissions, and on diesel fuel requirements for marine engines (covering sulfur content of fuels).


Who is covered by the regulations?

Emission requirements for marine engines apply most directly to engine manufacturers. However, owners and operators of vessels should be aware that remanufacturing an existing engine is covered under the regulations, and that by specifying the work to be done on an engine, the owners and operators of the engine are considered to be "remanufacturers", and are therefore responsible for ensuring that the work is done in compliance with the regulations.

What is the purpose of the regulations?

Exhaust from all internal combustion engines, including marine engines, contains several hazardous pollutants:

  • Particulate matter (soot): fine particles become trapped in the lungs and can lead to serious health effects, including breathing problems and cancer

  • Nitrogen oxides: lead to the formation of ozone, a component of smog that attacks lung tissue

  • Unburned hydrocarbons: react with nitrogen oxides in the presence of sunlight to form ozone

  • Carbon monoxide

  • Sulfur oxides: causes acid rain

Engine and pollution control technologies have been improving steadily, so modern engines emit much less than older models. The regulations are intended to ensure that new and remanufactured engines take advantage of advances in efficiency and emission control.


Marine engines are regulated according to size and type (diesel vs. gasoline).

Diesel (compression-ignition) engines. Current regulations recognize several size categories for compression ignition (diesel) marine engines. The numbers in parentheses indicate the section in the Code of Federal Regulations (CFR) under which each engine type is regulated:

  • Small (less than 37 KW = 50 HP). For this category, marine engines are treated like other nonroad Diesel engines (40 CFR part 89).

  • 37 - 130 KW (50 - 175 HP). Above 37 KW, special regulations apply specifically to marine engines. The details can be found in two parts of the Code of Federal Regulations (40 CFR part 94 and 40 CFR part 1042).

  • 130 - 600 KW (175 - 804 HP). Engines this size and larger are affected by international treaty obligations. U.S. regulations are found in 40 CFR part 1043.

  • 600 KW (804 HP) and above. Regulations being phased in by 2014 require catalytic exhaust treatment and the use of ultralow sulfur fuels.

The DieselNet website provides a detailed description of the standards.

Gasoline (spark ignition) engines are regulated under 40 CFR part 1045 (rules applying to engines manufactured before model year 2010 can be found at 40 CFR part 91). This category typically includes smaller and recreational vessels.

Most of the provisions in the standards apply to engine manufacturers, rather than to owners and operators of vessels equipped with the engines. But the regulations do specify several requirements that apply to owners and operators as well as to vessel manufacturers. Owners and operators must:

  • Comply with manufacturer specifications for emission controls requiring the use of specific fuels, lubricants, or other fluids

  • Report to EPA within 30 days whenever a vessel equipped with a selective catalytic reduction (SCR) system requiring the use of urea or other reductants is operated without the appropriate reductant

  • Allow authorized agencies to conduct required emission tests and inspections, and provide reasonable assistance to enable them to perform the tests or inspections

Special rules concerning operating conditions, recordkeeping, and reporting apply to owners and operators of large (Category 3) engines (see 40 CFR 1042.660).

More Resources

The DieselNet website provides summaries of U.S. and international standards that apply to diesel emissions from marine engines.