Optimising the engine-propeller matching for a liquefied natural gas carrier under rough weather

Dual-fuel Diesel engines have become the most interesting alternative for liquefied natural gas carriers (LNGCs) since they are able to use boil-off gas as fuel. However, there is a lack of studies about the optimisation of propulsion system selection considering weather conditions in an integrated approach. Thus, the present work aims to provide a comprehensive approach to perform the optimisation of engine-propeller matching for an LNGC under rough weather. A weather condition was included in the assessment of total resistance and thereby affected the propeller's open water efficiency, shaft speed and brake power. Constraints were included to the approach in order to avoid propellers that could present issues concerning strength, cavitation and vibration. A differential evolution optimisation algorithm was applied to minimise the fuel expenditure of propulsion for a round trip. The case study was designed using an LNGC with cargo capacity of 175,000 m(3) sailing in laden condition from Lake Charles to Tokyo Bay, via Panama Canal, and returning in ballast. All suitable matchings for 5346 propellers were found in 2.8 h and over 28% of them were constrained. The method has shown gains up to 19% of fuel expenditure reduction. The required brake power was approximately 20% higher for rough weather than for still water. Therefore, the approach used here has shown a significant gain and highlighted the value of exploring a broad range of propellers and engines in an integrated manner, as well as considering the weather condition.