Calm water resistance and self propulsion simulations including cavitation for an LNG carrier in extreme trim conditions

In recent years many studies and real-life applications dealing with trim optimisation have shown that operating a ship at small trim angles can improve the energy efficiency by up to 5% depending on ship speeds and loading conditions. This efficiency gain mainly results from the re-positioning of underwater hull features, such as the bulbous bow or the stern bulb. Different to the above described approach the present study deals with operating a LNG Carrier at an extreme bow-up trim angle of Ɵ = −1.9 deg. In order to predict the performance, URANS virtual towing tank simulations in calm water were performed for both, nominal resistance conditions and self-propulsion conditions including cavitation. The numerical results, including the ship resistance, the nominal propeller wake field and the simulation of propeller cavitation in self-propulsion conditions indicated a largely improved performance. Due to a significant reduction in nominal resistance by up to 27.5% the ship selfpropulsion point in extreme trim conditions was found at a lower propeller rotation rate compared to level trim conditions. This also reduced the cavitation volume and finally resulted in a delivered power reduction of up to 28.8%.