APPROACH A large number of cruise ships currently sailing must already – or will soon have to – comply with stricter environmental regulations, requiring the installation of scrubbers, the use of LNG as fuel, or a change­over from heavy fuel oil (HFO) to marine gas oil (MGO) or a combination of the two. The difference in price between MGO and the HFO now used can increase operational expenses by up to 40%. Making ships more energy-efficient and using distillate fuels to comply with the regulations is an option, but the financial attractiveness needs to be investigated for every ship on a case by case basis. A conversion to LNG might be, under certain circumstances, an attractive alternative that eliminates the complexities of fitting scrubbers and the high cost of burning distillate fuel. Alexandros Chiotopoulos, Atle Ellefsen and Gerd Michael Wuersig from the classification society DNV GL describe a novel approach to LNG conversion: elongating the vessel.