“The world’s 90,000 vessels burn approx 370 million tons of fuel per year emitting 20 million tons of Sulphur Oxides.”

The exhaust is 6% SO2? I am extremely skeptical of these figures. Most large ships use diesel engines. The fuel is not the same grade as automobiles but it is a long way from being waste oil. It has been established for decades that a large slow turning diesel is the least polluting of all petroleum engines in terms of pollutants per horsepower. The figure of 90,000 vessels includes vessels of all sizes. The number of large container ships and tankers is very much lower, a few hundred of each.