I think it's still the top 50% that make day 3 and get a key for the boat. I think the 1-in-100 represents one day one, when the tourney starts, you've got a 1-in-100 at that point.
Exactly what Charles said. Your chances on day 1 start at 1 out of 100 to win the boat but when you qualify for day 3 (top 50%), your chances double to 1 in 50.