Sorry to say that most trips have someone being sick but it is still worth taking one as I am sure you will find an area on the boat where you can sit without having to watch them.

It also depends on what you want to see. I was there last June and went on the submarine safari. It is a purpose built yellow sub, air conditioned with plenty of seating.
Nobody was sick either. At the end of the trip you are also presented with a certificate to say you have been. Something fun and different if you have kids, or are a kid at heart yourself.

Be careful when booking from one of the reps on the front of Porta Colon, they showed us photo's of a luxury catamaran with bar & loads of seating but when it came to it was much smaller with no seating & so full everyone were cramped on the boats netting that forms the deck. The sea was very choppy, loads of people were spewing all over, I was never so glad to see Terra Firma after the 3 hours. But do you know what looking back, I enjoyed it in a masachistic way!