IMO introduced Energy Efficiency Design Index (EEDI) to regulate the greenhouse gas (GHG) emissions from ships. The cheapest and easiest way to fulfil the EEDI requirement is to reduce installed power for most ships. Therefore, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements and not consider ship safety in a satisfactory way. This could induce ship manoeuvrability and safety problems in adverse seas, which needs urgent investigations on minimum power to maintain ship manoeuvrability in adverse sea.

A time domain code ‘Waqum’ has been developed based on the force superposition of unified theory to study the minimum required power for maintaining ship manoeuvring ability in adverse sea states. The code combines sea-keeping and maneuvering equations, together with an engine model to predict ship responses in waves. The code can help us to study ship responses in transit situation and give us better insight into ship maneuvering ability in adverse sea states. In order to improve the simulation speed, the time domain code does not calculate all the hydrodynamic forces directly. Thus, some precalculations should be done for some force components before launching the simulation for a new ship. Therefore, the methodology and accuracy of each force component will influence the accuracy of the manoeuvring code. The methodology for determining each force component will be discussed, especially the identification of maneuvering derivatives based on CFD simulations. The code has been improved recently, and another rudder model has been implemented. Further, the the code with new rudder model is verified in calm water. The code’s ability to capture ship maneuvering in waves is also demonstrated.

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