Windsurfing   Obstruction : An object that a boat could not pass without changing course  substantially, if she were sailing directly towards it and one of her hull lengths from it.  An object that can be safely passed on only one side and an area so designated by the  sailing instructions are also obstructions. $_{ }$  Postpone : A postponed race is delayed before its scheduled start but may be started  or abandoned later.$_{ }$  Course : A course a boat would sail to finish as soon as possible in the absence of the  other boats referred to in the rule using the term. A boat has no proper course before  her starting signal. $_{ }$  Racing : A boat is racing from her preparatory signal until she finishes and clears the  finishing line and marks or retires, or until the race committee signals a general recall,  postponement or abandonment. $_{ }$  Room : The space a boat needs in the existing conditions, including space to comply  with her obligations while maneuvering promptly in a seamanlike way. $_{ }$ 9 