Assuming the weather is nice, it is a big enough vessel that you should not have a problem. There is not much to see unless you like water. You can see the cruise ships behind you and Playa Del Carmen in front of you. They have air conditioned inside rooms with tables (we played cards) to passt the time. It takes about 30 mins our so to cross.
Or you can sit outside and enjoy the breeze and the sun. (they also have a snack bar)
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007