As a management level engineering officer on a motor vessel equipped with engines capable of burning both high sulfur content residual fuels and low sulfur content distillate fuels, on approaching arrival to a US port, for planning purposes, what must be done?

Correct Answer: Option B — The fuel changeover is commenced BEFORE the vessel enters the SOx emissions control area to allow time for the high sulfur fuel to be flushed out of the fuel lines.

Fuel changeover requires time to flush high-sulfur residual fuel from the system and stabilize the engine on low-sulfur distillate. Commencing the procedure before entering the Emission Control Area ensures that the fuel lines are fully purged and the vessel is in full compliance the moment it crosses the boundary.