Environment and regulation

The dates that fix an engine NOx Tier and what a major conversion does to them (MARPOL Annex VI Regulation 13)

For a ship built in 2006, replacing an engine may change the applicable NOx Tier. The original construction date and the type of major conversion determine which date and standard apply.

MARPOL Annex VI Regulation 13 generally uses the ship’s construction date rather than the engine’s manufacturing year. Major conversions can change the applicable date depending on the work performed.

This article does not deal with the emission limits themselves. It looks only at the dates that decide which Tier applies.

The ship construction date determines the applicable Tier

3 Subject to regulation 3 of this Annex, the operation of a marine diesel engine that is installed on a ship constructed on or after 1 January 2000 and prior to 1 January 2011 is prohibited, except when the emission of nitrogen oxides (calculated as the total weighted emission of NO2) from the engine is within the following limits, where n = rated engine speed (crankshaft revolutions per minute):

The subject is the engine, and the conditional clause points at the ship: installed on a ship constructed on or after 1 January 2000. When the engine itself was built is not in that sentence.

Paragraph 4 sets the next bracket with the same structure. An engine installed on a ship constructed on or after 1 January 2011 is Tier II. The bracket ahead of it is a ship constructed on or after 1 January 2000 and before 1 January 2011, and that place is Tier I.

The application has an engine-side condition too. Regulation 13 bites only on a marine diesel engine with a power output of more than 130 kW (paragraph 1.1.1). Engines used solely for emergencies and engines installed in lifeboats are out (paragraph 1.2.1).

Tier III lays a sea area on top of the construction date

5.1 Subject to regulation 3 of this Annex, in an emission control area designated for Tier III NOx control under paragraph 6 of this regulation (NOx Tier III emission control area), the operation of a marine diesel engine that is installed on a ship is prohibited:

Tier I and Tier II apply wherever the ship is. Tier III applies only inside a designated area. So the finding takes one more condition. The date the ship was constructed, and the area the ship is in right now.

Sea area	Ships Tier III bites on there
North American Emission Control Area, United States Caribbean Sea Emission Control Area	Constructed on or after 1 January 2016
Baltic Sea Emission Control Area, North Sea Emission Control Area	Constructed on or after 1 January 2021
Any other designated NOx Tier III area	Constructed on or after the adoption date of that area, or a later date if the designating amendment sets one

When the same ship moves in and out of the area, the standard that applies changes. That is why paragraph 5.3 requires a record. On entry into and exit from the area, and when the on/off status changes inside it, the tier and the status of the engine go into the logbook or electronic record book prescribed by the Administration, together with the date, time and position.

Separate the general construction definition from the Norwegian Sea rule

Construction normally means keel laying or reaching a similar stage of construction. A ship with a 2010 keel date and 2012 delivery therefore falls under the general Tier I construction bracket.

MEPC.392(82) gives the Norwegian Sea a specific Tier III rule: a building contract on or after 2026-03-01; without a contract, keel laying on or after 2026-09-01; or delivery on or after 2030-03-01. The Canadian Arctic threshold is construction on or after 2025-01-01. The designation amendments entered into force on 2026-03-01. Do not apply the 12-month SOx exemption to NOx Tier III.

Regulation 13 defines major conversion inside itself

2.1 For the purpose of this regulation, major conversion means a modification on or after 1 January 2000 of a marine diesel engine that has not already been certified to the standards set forth in paragraph 3, 4 or 5.1.1 of this regulation where:

It opens with For the purpose of this regulation. The definition is used inside Regulation 13 only. The target is narrow as well. An engine already certified to the standards in paragraph 3, paragraph 4 or paragraph 5.1.1 falls outside it.

One of three things makes it a major conversion.

The engine is replaced by another engine, or an additional engine is installed (paragraph 2.1.1)
A substantial modification as defined in the revised NOx Technical Code 2008 is made to the engine (paragraph 2.1.2)
The maximum continuous rating is raised by more than 10% over the value of the original certification (paragraph 2.1.3)

The application provision uses the same date. Paragraph 1.1.2 brings an engine that undergoes a major conversion on or after 1 January 2000 inside Regulation 13. There is one way out of it. The Administration is satisfied that the engine going aboard is an identical replacement for the one it replaces. Whether it is identical is decided by the Administration, not by the company.

Swap the engine and the conversion date applies, rework it and the ship’s date applies

2.2 For a major conversion involving the replacement of a marine diesel engine with a non-identical marine diesel engine, or the installation of an additional marine diesel engine, the standards in this regulation at the time of the replacement or addition of the engine shall apply.

Replacement and addition take the standards of the time of the conversion. Even on a ship constructed in 2006, changing to a different engine today brings today’s standards. The next sentence of the same paragraph opens one relief, and only for replacement engines. If the replacement engine cannot meet the standards in paragraph 5.1.1, it has to meet the Tier II standards in paragraph 4, taking into account the guidelines developed by the Organization. Installing an additional engine gets no such relief.

The other two run the other way.

2.3 A marine diesel engine referred to in paragraph 2.1.2 or 2.1.3 of this regulation shall meet the following standards: .1 for ships constructed prior to 1 January 2000, the standards set forth in paragraph 3 of this regulation shall apply; and .2 for ships constructed on or after 1 January 2000, the standards in force at the time the ship was constructed shall apply.

A substantial modification and an increase in the maximum continuous rating do not climb to the standards of the day the work was done. They fall back to the date the ship was constructed. For a ship constructed before 1 January 2000 it is paragraph 3, which is Tier I. For a ship constructed after that, it is the standards in force when the ship was constructed.

One phrase, major conversion, splits in two here. Swap the whole engine or add one, and the date is made by the conversion rather than by the ship. Stop at reworking the engine that is already there, and the date is the construction date of the ship again. So the record of the work has to say what was done. The date on its own does not settle the bracket.

Worth confirming

The passages above come from the consolidated MARPOL Annex VI (resolution MEPC.328(76)). Regulation 13 sits on printed pages 22 to 27, and the definitions in Regulation 2 on pages 4 to 10. The emission limits are not reproduced here, because the values and the formula change with the rated speed band. Read them in the original.

Three things are left over. What counts as a substantial modification is set by the revised NOx Technical Code 2008. Regulation 2 paragraph 2.17 carries a major conversion definition as well, but that one is written for chapter 4 (energy efficiency) and is a different thing from the Regulation 13 definition. And the Administration can open two exclusions. One is an engine on a ship engaged solely on voyages within flag State waters where the Administration has established an alternative NOx control measure (paragraph 1.2.2). The other is an engine installed on a ship constructed, or an engine converted, before 19 May 2005, where the ship trades only to ports and offshore terminals of its flag State (paragraph 1.3).

The NOx Technical Code certification amendments in MEPC.398(83) also entered into force on 2026-09-01. For a substantially modified engine or certification to a Tier not certified at installation, check the amendment’s applicability and approval procedures alongside the construction-date rules.

You can consult the cited source documents

These links lead to the official publishers of the documents discussed here. Match the edition and provisions cited in the article, and check subsequent amendments and flag-state implementation before applying them.

Scattered records hide the pattern

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