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Nonroad Engines, Equipment, and Vehicles

Diesel Boats and Ships

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Marine diesel engines are used in a variety of different types of vessels ranging in size and application from small recreational runabouts to large ocean-going vessels. New marine diesel engines must meet increasingly stringent emissions requirements, yet these engines continue to emit significant amounts of oxides of nitrogen (NOx) and particulate matter (PM), both of which contribute to serious public health problems.

In May 2004, as part of the Nonroad Diesel Tier 4 Rule, EPA finalized new requirements that decrease the allowable levels of sulfur in marine diesel fuel by 99 percent. These fuel improvements, which began to take effect in 2007, are creating significant environmental and public health benefits by reducing PM from new and existing engines.

In March 2008, EPA finalized a three-part program that further reduces emissions from marine diesel engines with per-cylinder displacement below 30 liters. These include marine propulsion engines used on vessels from recreational and small fishing boats to towboats, tugboats and Great Lake freighters, and marine auxiliary engines ranging from small generator sets to large generator sets on ocean-going vessels. The rule will cut PM emissions from these engines by as much as 90 percent and NOx emissions by as much as 80 percent when fully implemented.

The 2008 final rule includes the first-ever national emission standards for existing commercial marine diesel engines, applying to engines larger than 600kW when they are remanufactured (PDF) (7 pp, 160k, EPA_420-F-09-003, February 2009). The rule also sets Tier 3 emissions standards for newly built engines that are phasing in from 2009. Finally, the rule establishes Tier 4 standards for newly built commercial marine diesel engines above 600kW, based on the application of high-efficiency catalytic aftertreatment technology, phasing in beginning in 2014.

The Ocean Vessels and Large Ships page includes information on U.S. regulations for Category 3 marine diesel engines as well as the international treaty called MARPOL Annex VI with standards that apply for marine diesel engines over 130 kW. Information is also available on Gasoline Boats and Personal Watercrafts.


See the electronic Code of Federal Regulations (e-CFR) for the full text of current regulations that apply to marine diesel engines and vessels:

40 CFR part 1042 Emission Standards and Certification Requirements—Tier 3 and Tier 4
40 CFR part 94 Emission Standards and Certification Requirements—Tier 1 and Tier 2 for engines at or above 37 kW
40 CFR part 89 Emission Standards and Certification Requirements—Tier 1 and Tier 2 for engines below 37 kW
40 CFR part 1065 Engine Exhaust Emission Test Procedures
40 CFR part 1068 General Compliance Provisions
40 CFR part 1043 Regulations implementing MARPOL Annex VI, including requirements for in-use fuels, engines above 130 kW, and vessels with those engines

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Certification Guidance Documents

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Emission Inventory Publications

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