This practice has been continuously enhanced since its implementation in 2013, resulting in significant reductions in fuel consumption. In 2017 alone, 81 operations were performed.
The divers spend around three to four hours polishing the propeller to achieve a Grade A on the Rupert Roughness Comparator Scale. Studies from NTNU (Norwegian University of Science and Technology) conclude that moving from grade E to A on the Rupert scale can increase speed by more than 0.5 knots. For a voyage from Panama to Yokohama, this can equal a fuel consumption reduction of more than 100 tonnes and as a consequence, a reduction in CO2 and SOx emissions.
Diver performing propeller polish on Bow Tribute, January 2017. Photo: IMS Diving