On October 2, 2020, the U.S. Environmental Protection Agency (EPA) issued a final rule amending the national marine diesel engine program set forth in 40 C.F.R. Part 1042. Through the amendment, EPA is providing boat manufacturers additional lead time to install Tier 4 marine diesel engines in certain high-speed commercial vessels. Tier 4 standards — applicable to marine diesel engines at or above 600 kilowatts — were expected to be phased in between 2014 and 2017 and were based on achieving emissions reductions through aftertreatment technology, such as selective catalytic reduction. While these engines are mostly used in various types of large workboats and passenger vessels, certain engines are used in high-speed vessels that need compact and powerful engine designs. After the Tier 4 standards were fully in effect, some high-speed boat manufacturers informed EPA that they were unable to find certified Tier 4 engines with suitable performance characteristics for the vessels they needed to build.