For WWW3 model it seems to be different (March 2019): https://github.com/NOAA-EMC/WW3/wiki/Manual
« The model [....] computes other transformation processes such as the effects of surface currents to wind and wave fields, and sub-grid blocking due to unresolved islands »
« 3.9 Winds and currents
Model input mainly consists of wind and current fields. Within the model, winds and currents are updated at every time step ∆tg and represent values at the end of the time step considered. »
In any case it would be much better for you to sail downwind and down swell. But this is quite tricky in the Agulhas current area, the swell being mostly from SW. Don’t you plan a stop in Durban?