Lots of great info here, but here's the answer to the OP's question! Most people get sicker quicker on a power boat - especially a slower one - than on a sailboat IF THE SAILBOAT IS SAILING, WITH SOME WIND! The difference is the motion: a (slower) power boat moves in a circular roll, like a cork, and that 3D motion is tougher for our brains to resolve. A sailboat that's sailing is usually held at a relatively constant heal angle by the wind in the sails, so it can only move in a flat 2D pitching movement, no rolling. Put a sailboat out into calm wind with big ocean waves or leftover lake waves from past wind, and it moves 3D spherically like a powerboat and more people toss! If you hear external halyards slapping against the mast, keep your eyes on the horizon!
BTW, most of us have the gene/trait that makes us sick if our visual and vestibular motion signals don't match, because it's SURVIVAL ENHANCING!! Especially (pre-)historically, if those signals don't match, it's very likely because you ate something that had spoiled, or was otherwise toxic! So the "smart" thing to do is to toss it before it kills you. We are the descendants of people who survived eating the bad mushrooms or meat, and we inherited their survival trait. (When I do get queasy, I feel a little better just knowing this!)
And it seems contradictory - but ISN'T - that being below makes people sicker, but taking a nap below makes them recover: Closing your eyes makes the sensory mismatch go away! But when you sit down below, your eyes tell you that you're in a stationary room, and your inner ear tells you you're moving around. So your inheritance tells you to lose your lunch because it might be toxic!
And fear vs. confidence is also huge, and reminds me of a personal experience: I was on an airplane flying from Toronto to NYC or Boston. Terrible rough flight. I was just taking the one flight, but it was connecting with a flight to Portugal, and most of the passengers were Portuguese relatives returning home after visiting family in Toronto for Christmas or Easter. A LOT of them spoke little English or French. When the nasty turbulence began, it was accompanied by serious announcements in both official Canadian languages, but NOT Portuguese! The linguistic correlation with cookie-tossing was ~perfect!