Agree with Mike - the guy was singlehanding on a Taipan, flipped and became separated. We saw the boat on its side, but nobody on it. We started scanning the area, but the sea state was large enough that we didn't see him until after we heard the whistle. Picked him up and transferred him to the USCG who rolled up just then. That was one scary race, but it convinced me to always carry a whistle. Doesn't have to be special. Just loud.