Rule 23.1 states, "If reasonably possible, a boat not racing shall not interfere with a boat that is racing." What does "interfere with" mean in this rule? No ISAF Case or US Appeal provides guidance, so here's my opinion. "Interfere with" has, according to dictionaries, quite a broad range of meanings. These include affect, hinder, hamper, and obstruct. You would clearly interfere with another boat if you got in her way and she had to change course to avoid you, but you would also interfere with her if you back-winded or blanketed her. You could interfere with her well before you got so close that she had to take avoiding action.