[mkgmap-dev] Problematic routing on road_class=3 ferry routes for hikers

In the Belgium OSM forum someone reported that in the hiking profile ferry connections are avoided. http://forum.openstreetmap.org/viewtopic.php?id=26980 I noticed in Basecamp that the road_class=3 might be the reason for this (=main highways). In the internal routing routines of the Garmin Oregon, these roads are blocked by default for hiking (but not in the pedestrian mode). Solution would be to assign ferries that are blocked for motorcars (tagged on osm with motorcar/motor_vehicle=no) with road_class=0 instead of 3. Can this be done in the default line style? I can't find any route=ferry strings in the lines nor access files anymore. Where does mkgmap set this road_class?