There are actually three ferry companies operating from Playa to Cozumel; Mexico Water Jets, Ultramar and Barcos Caribe.
The schedule changes daily and is sometimes affected by weather.
Buy a one-way ticket for the next ferry. The companies alternate departures, buying a round trip could delay your return. There is no savings Discount on a round trip ticket.
Barcos Caribe Ultramar Mexico Waterjets 
