Winjet - Fast Ferry | Cozumel - Playa del Carmen and Routes and Timetables :: Ultramar
It looks like they are still alternating days with the two companies, but up to six a day now.
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Ultramar will let me buy a ticket now for September 4th. Winjet won't let me buy anything after August 31. Should I buy now, not knowing exactly what time I will get to the ferry dock? By the every other day schedule, that should be a Winjet day.