The nursery rhyme Rub-a-dub-dub tells a tale of three men who sail out to sea in a tub. An updated children’s song, Scrub-a-dub-dub, moves it along with the line “sitting in the tub, getting so clean like a washing machine”.

The new version could be a mantra for the proponents of scrubbers for cleaning sulphur from ships’ exhaust gases. An operator’s representative at a seminar on the technology last year even went so far as to say: “A scrubber is a very big washing machine”.