It won't really matter as once you get off the ferry the device will know where it is and recalculate the route from your exact position to the destination (as this won't have changed) you can then follow it as you continue your trip.
If you are seeing it planning a strange route while sat at home don't worry too much as not all ferry crossings will be in the map data and the device usually only has one crossing per port. Most newer units tend to send everyone to the channel tunnel these days!! But with a little working out its not difficult to set a different port as an intermediate stop - Mike |