This is an area where a specialist broker can really help you out.
The question is actually far more detailed than “does your policy provide cover for competing in yacht races?”.
It might apply to a race undertaken in a specific area such as club events on Moreton Bay. That will have different ramifications to races in Hamilton or Airlie Beach race weeks which in turn will be regarded differently to a major bluewater race such as Sydney-Hobart.
Are you insuring for a series or just a single race?
I also know of a case where a businessman left the job of insuring his boat up to the company’s in-house accountant. As a result, he paid higher race yacht premiums for three years, when he never even competed in a single race.
His accountant should have changed the cover back to ‘normal use’.