I'm also prone to seasickness. We did an Antarctic cruise a few years back on one of the big Princess ships. Crossing wasn't bad in either direction with seas+waves running about 30-40' with 30-50 knot winds during the crossing. That's the advantage if a large ship as on a smaller one those conditions are going to be rough on small ships. The disadvantage is that there wasn't an opportunity to go ashore. Because of the weather, I'd be worried about the entire trip being a bust unless I planned to be able to sit around in Punta Arenas for a week or so waiting for the weather to clear.
I'm a big believer in the scopolamine patch. Works great for me with only a bit of sleepiness and having to forego alcohol. I'd think that the sick bay in any large ship is going to have powerful anti-nausea drugs for anybody that moves beyond feeling miserable to a real medical problem. If I got to that point (think throwing up blood), I think I'd want to be under the care of the on-board doctor.
As many have noted, don't wait until you feel bad. Plan ahead and take action the day before.