An event with that many participants should never end up with 300+ dnfs ... compare the costs of adding a day to the overall cost of attending to the owners ... Put the event on for three days and run it on the most promising day for conditions.
On our Gulf Coast we have accused yacht clubs of shortchanging competitors on the water and overcharging at the bar for food and beverages.
Yeah, but it's kinda hard to tell an event that has the attendance of 300+ competitors that they're doing it wrong, though!
