A substantial modification only holds up if the emissions can be proven

What the rule closes

MEPC.398(83) amends the NOx Technical Code 2008. It closes a gap: a defined route for certifying an engine after a substantial modification, or when it is brought to a Tier it did not hold at installation.

The limits are unchanged. What is new is the route, and that the test is performed on the installed engine. The Norwegian Maritime Authority has implemented the amendments in Norwegian law from the same date, and notes that certification is to a large extent delegated to the recognised classification societies.

When the engine has moved off its baseline

A modification that changes the NOx-relevant configuration moves the engine off its certified baseline. Examples are dual-fuel or methanol conversion, Tier III SCR, a fixed or variable compression ratio, turbocharger cut-out and part-load tuning. Whether a given change counts as a substantial modification is assessed together with class.

From that point the test bed certification no longer proves compliance, and there is no test bed to return to. Compliance has to be shown where the engine runs, onboard.

What the route looks like

The procedure applies to the installed engine, so the engine is tested onboard. It can cover a single engine, or an engine group represented by its parent engine, but not an engine family. The other engines in the group follow as member engines, with a parameter check instead of a full emission measurement.

The 100 % load point may be as low as 85 % of rated power, if the test plan allows it. The test plan is agreed with the Administration before the test, and the nameplate is replaced if power or speed changes.

A change of Tier level means a new Technical File. An amendment is used to update an existing file.

Prove it once, onboard

The measurement has to stand up to survey. Not measure and hope, but a known result built in from day one: the test plan agreed before the test, the equipment calibrated to NTC 2008, and class aligned before the measurement.

Depending on the engine, the scope can include NOx and the full gaseous bench (CO, CO₂, O₂, THC), and methane slip (CH₄) and N₂O where the fuel makes them relevant. The measurement follows NTC 2008 and ISO 8178 and, where the trade requires it, EPA 40 CFR Part 1042 and 1065.

Where we come in

We support the whole process, in close collaboration with the engine designer, the owner, the crew and class: preparation, the test plan, the measurements, the optimisation of the engine from the measured results, and the documentation for the amendment or the new Technical File, including documentation for EIAPP re-issue and SCR verification.

What we recommend

Bring the measurement and certification scope in from the start, and the outcome is known before the vessel returns to service, not discovered at survey. Talk to class and the engine designer before the scope is fixed. It is the cheapest point to get it right.

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