You need to count only time to load/unload a train. It's not like unload the ship and then load train. Trains would go as soon as they are loaded, so 4 days for

You need to count only time to load/unload a train. It's not like unload the ship and then load train. Trains would go as soon as they are loaded, so 4 days for unloading a ship means 10 trains a day from one ship.