why don't you call the cruise line and ask? i'm sure it's a pretty common question if your going to be stopping at ports which have good surf.
Some boats (I believe Carnival) have the flowrider wave machines on the boat. Don't even have to get off. However I am sure those machines would get old after a while and it is either expensive, or the lines are long.
Yeah...It's Carnival. The flowrider is cool for what it is. But, your gonna want to bring your boards if allowed and surf real waves. Flowrider is fun....but it isn't surfing. *edit