Over 80% of global trade is carried by sea. With more than 125,000 commercial and naval vessels operating around the world, ship-engine emissions are projected to rise by 250% by 2050 unless controls are imposed. Pollution from ship engines is so significant that in 2016 the International Maritime Organization (IMO) issued “IMO 2020 Rule” to cut fuel sulphur content 86% by the year 2020. A component of acid rain, sulphur oxide (SOx) emissions contribute to ocean acidification that harms marine habitats and ecosystems. To comply with IMO 2020, commercial vessel operators and owners have two routes to take.