is inside land...
But even if you move it in water
you cannot expect the routing module to drive you up to the cat-way
The routing module is intented for relatively long distances where you must take decision concerning weather
. You can put your destination point somewhere close the the entrance of the harbour and probably qtvlm will find a solution.
What you can do otherwise is the create a route manually (route->create) insert a few POIs and you will get a rather precise estimation of the travel duration.
For instance, moving a bit your destination point outside the harbour: