What version of OsmAnd are you using, on what device and Android/iOS version? 3.5.3 on Android 9
Please, do the routing in nautical maps only linea recta from waypoint to waypoint and not attempt to find a route over roads. Nautical navigation works in a very different way and offering it in this way is how one would use a (analog) nautical map and routing over streets is just not of any use.
Currently OsmAnd doesn't support "straight line" boat navigation (cause it should then take into account islands and lands) - so it uses only OSM data such as (waterway=fairway)
What version of OsmAnd are you using, on what device and Android/iOS version? 3.5.3 on Android 9
Please, do the routing in nautical maps only linea recta from waypoint to waypoint and not attempt to find a route over roads. Nautical navigation works in a very different way and offering it in this way is how one would use a (analog) nautical map and routing over streets is just not of any use.