We had some funny wind during a race once. Coming up to the finish mark, (Take your own time passing within 75' of it when it bears 360º) doing about six knots upwind on starboard, when I notice the wind's riffles on the water stop in a zone about 100 yards away from the mark. We proceed at six knots to sail into an absolutely flat calm. We stop, lose steerage way, and get spun around by the tide several times before the current carries us back into the breeze. We gybe around, sheet in, pick up speed to six knots again... and sail back into the absolutely flat calm. This happened three times, with competitors coming up from behind and having the same thing happen to them. Finally, we decided to stay in the breeze well past the mark so that the tide would carry us towards it, instead of away from it, when we sailed out of it, and we were able to finish. Very strange.