On map seed 319e04, it is possible (from the settlements that actually do have a port) to take a ship to Eulenkrug, which, however, has no port of its own (despite being right on the coast). This doesn’t normally happen with settlements that are right on the coast but with no port. I’m not sure if Eulenkrug had originally had a port that had just been destroyed, but its description has it as a regular lumbar village with no suggestion of any port, and the only ruined site adjacent to the village was a little bit away from the coast.