Retrofitting multiple technologies at the same time is likely to prove the best results in cutting fuel consumption but is a complex business as ships vary so much and are often not built to facilitate upgrading.

Hapag-Lloyd has a programme to fit new propellers to 80 existing container ships as they go into drydock so that they will be more efficient at lower service speeds, and that also requires adding new bulbous bows at the same time, said the German liner group’s deputy head of strategic asset projects, Christoph Thiem.