Comparison of ship’s speed loss in waves in some numerical simulation methods

Abstract

This study evaluates the difference in speed loss, engine power, and fuel oil consumption of a bulk carrier from the viewpoint of weather routing. The evaluation of speed loss is important as speed loss influences accurate ship operation. The evaluation of speed loss is based on seakeeping and machinery theories. Speed loss due to added resistance is evaluated by different simulation methods, and the results are compared. Furthermore, to reproduce actual operations, three types of engine controls are considered. Numerical simulations for evaluating speed loss are carried out for a 20,000DWT-class bulk carrier in irregular wave patterns. No significant difference is observed in speed losses evaluated using the enhanced unified theory and new strip method when the mean wave period is longer. However, NSM underestimates speed loss if the mean wave period is relatively shorter. In addition, it is known that asymptotic formulae contribute accurate evaluations in a short period of waves. It is possible to implicitly evaluate speed loss under actual situations if these seakeeping models are combined with propulsion and engine control models. This study conducts basic research on this possibility to improve safe and efficient operation of vessels in rough seas.