Ships don't use free harbors?

[Varg]

Is there no way for the game to automatically determine if there's a free harbor the ships can use?
Do I really have to alter every trade route and update them to use the pier or harbor masters docking?

[Helgart]

Place more piers for your harbour area to be free more often. Harbour master office may be used to create a harbour area on the opposite side of your big island to establish shorter trade routes on this direction.

[Helgart]

If you let ships to choose between distant harbours of the same island, which in rotation become either free or busy and ships will never reach those but roam like a pendulum. Just assign the route point to a warehouse and wait until it's free