Such a hard-to-reach shipyard...

True... I also haven't seen a shipyard anywhere except in the places where it should be according to the scenario (for example, in the regular Heroes 5, campaign 2, mission 4). But once, I played on a multiplayer map, and there was a small lake in the Dungeon; there wasn't even a place to swim, but a Castle was standing nearby, and I built a shipyard there just out of curiosity. The management is the same as usual: you enter, pay, and a ship appears... And in multiplayer, there can't be a shipyard in cities at all; it would be an unfair advantage (although level 15 for a city to have a shipyard is a bit much):)