Hello SueWheldon,
Just back from a NZ-Aus cruise on Odyssey. As mentioned above, the classes were usually around 7 or 8am - yoga, pilates and then again around 5pm - stretching, yoga, pilates. Nothing very vigorous. You sign up at the spa reception desk.
I use the Les Mills on demand system and followed some programs I had downloaded on my iPad, using hand weights in the gym. The gym is reasonably well equipped, but not very spacious; there is some space at one end to do your own thing, away from the treadmills, steppers and bikes. You can also use the Motion Studio (which has a rack of hand weights) if nobody has a private session in there - just ask at the spa reception desk. I had that to myself and it was much better than the squeezy gym area.