I don't think it makes much sense to be required to fly a protest flag in a distance race. The purpose of the flag is supposed to be as a notice to the boat that is protested, and it is supposed to be visible to the boat that is protested. But in a distance race, you might see someone sail an improper course way ahead of you (or behind you, and you might never get close enough to that boat for them to see your protest flag or for you to hail them verbally.