Instead of starting the fleet all at the same time a Pursuit race sends boats off at the start at differant times depending on their Portsmouth Yardstick (PY) rating.  The slower classes are started first then the faster classes and finally the fastest classes are started.  In theory all boats should finish at the same time.  A boat's finish place is it's position in the fleet at the finish bell.  Pursuit races are generally run as a second race after the fleet race on Tuesday evenings during the summer months.