Trim optimisation in waves

The trim optimisation is nowadays a common practice for all ship owners. Reduction o fuel consumption and improvement of ship energy efficiency concern all sectors of the maritime industry. The trim optimisation consists in finding the best trim angle with regards to the lowest power - i.e. fuel consumption - for a given operating condition (loading condition and speed). Although the operational efficiency of trim optimisation based on calm water resistance computations databases could be proven at sea, it is well known that added resistance due to wave can significantly impact fuel consumption. The increase of cluster computing power make it today possible to evaluate the added resistance in waves using state of the art free surface RANSE solvers. This study of the optimal trim depending on the sea- states show that taking into account the waves could have a significant impact on the optimal trim that have been identify on still water. Although the optimal trim angle trends are the same on still water and in waves for low sea-states, for highest sea-states the trends can be the perfect opposite. This study shows that the optimal trim mainly depends on the draft and the sea-state. The speed seems to have an effect on the gains / losses amplitude but not on the best trim value. The in waves databases will enable operators to predict their ship efficiency with better accuracy, taking into account weather predictions. The trim needs to be therefore adapted regularly depending on the weather conditions the ship encounter during her voyage