ORS does not calculate any route with ferry over the baltic sea for trucks (hgv profile). I tried to calculate routes from Sweden to Germany and Poland, and no route using a ferry was found.
I think there is a difference between requesting a shortest or a recommended route. In general, ferries are a bit difficult for routing, as we have no idea how to get reliable travel times for ferry connections (e.g., schedule, time for onboarding). The shortest weighting works well because the travel time is irrelevant in this case.
May I ask you something else, the ‘profile’ parameter does not allow to route ‘train’ or ‘inland vessel’, it is not possible today, or even not planned, to have also the capability to route trains and/or ships as well ?
We have experimental support for public transport (in combination with pedestrian profile) but this is only working within a single time zone. We have no plans yet for a global solution.