We did this last summer and loved it! My mom tends to get motion sickness but I don't think she took Dramamine before going. She was fine. I tend to get a little queasy but was also fine.
Definitely do the open boat. Even my hard to please teen boys loved it. The little kid behind me was very scared though. I recommend that you prepare your son for the HUGE waves of water that will crash over him.
Have a great time.