If you are lucky enough to own a boat, there is good news. There’s plenty of space in Chicago’s harbor system. According to figures supplied by the Chicago Park District, total occupancy in the district’s 5,740 docking spots is just 74.3 percent. At an average docking fee of $5,000 or so a year, that means the nearly 1,500 vacancies are costing the Park District well over $7 million a year.