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
