With apologies for being late to this thread:
I've tried just about everything. The "natural" and non-drug approaches (ginger, ginseng, wrist bands, etc) do not help me at all. Bonine helps a little bit, but not much. The best thing I've found is scopolamine, and I'll still get sick if the seas are too rough. Six-foot seas would be way too rough for me, even with scopolamine.
The reason I'm posting this is to relate my experiences with scopolamine:
I've used the patch, and the tablet form of this drug.
The problem with the patch is that, at least for me, I get too high a dosage the first day and not enough the third day. With too high a dose (day 1) I get a very dry throat, which becomes a severe sore throat in dry weather, though it's tolerable in very humid weather, and I become very dizzy. Curiously, the dizziness caused by the scopolamine does not make me feel seasick, though as mentioned, severe motion will still make me sick. By the third day, the dosage is too low and even mild motion will make me sick. The patch, of course, is designed to be worn for three days, and then replaced if you are still on the boat.
The tablet form is the same drug. It used to be sold in the U.S. as Scopace, but that's no longer available as far as I know, but can be purchased over the counter in Australia as Kwells. Same drug. Kwells contains a lower dosage than Scopace did.
The disadvantage of the tablet form is that it only lasts about 8 hours and then must be repeated. The advantage is that you have control over the dosage, as you can split the tablets or take two. For day trips the 8-hour duration is an advantage. You can buy Kwells by mail from Australia. I now use it for long car or plane trips (if I'm not driving) instead of Bonine.
I hope this helps. Seasickness is one of the worst experiences I've ever had.