Applicable to all vessels with keel-laying on or after January 1st 2016 with an engine output of ≥130kW.

IMO NOx Tier III requirements will take effect in North American and US Caribbean ECAs from January 1st 2016 for vessels with a keel-laying date on or after January 1st 2016 and an engine output of ≥130kW.

If other ECAs for NOx are implemented, the NOx Tier III requirements will not be retroactive. That is, if new NOx ECAs take effect (e.g. for the North Sea and Baltic Sea), the Tier III emission limits become applicable to vessels with keel-laying as of the date the new NOx ECAs go into effect.

As per Regulation 13 of Annex VI to MARPOL 73/78 in an Emission Control Area (ECA) designated for Tier II NOx control, the operation of a marine diesel engine that is installed on a ship is prohibited except when the emission of nitrogen oxides (calculated as the total weighted emission of NOx) from the engine is within the following limits, where n = rated engine speed (crankshaft revolutions per minute):

* 4 g/kWh when n is less than 130 rpm;

* 9 · n(–0.2) g/kWh when n is 130 or more but less than 2,000 rpm;

* 0 g/kWh when n is 2,000 rpm or more;

As per MEPC.251(66) the above Tier III requirements shall apply as follow:

* to ships constructed on or after January 1, 2016 and operating in the North American ECA or the United States Caribbean Sea ECA;

* ships operating in an ECA designated for Tier III NOx control, other than an ECA described in paragraph 5.1.2 of Regulation 13 of Annex VI to MARPOL 73/78, and is constructed on or after the date of adoption of such an emission control area, or a later date as may be specified in the amendment designating the NOx Tier III emission control area, whichever is later.

A new subparagraph – number 3 – has been implemented in paragraph 5.2 through MEPC.251(66) stating that the requirements of Tier III shall not apply to a marine diesel engine installed on a ship constructed prior to January 1, 2021 of less than 500 gross tonnage, with a length (L), as defined in regulation 1.19 of Annex I MARPOL 73/78, of 24 m or over when it has been specifically designed, and is used solely, for recreational purposes.