Agree that Scop patches are the most effective prevention. My wife gets sea sick something awful. One night off the Tortugas I tied her to the boat to keep her from climbing overboard and drowning herself. Another night in the Bahamas I took a gun away from her to keep her from shooting herself, and tied her down again. Since she discovered Scopolomine both of our lives have been better! No more suicidal episodes. Years of operating a charter boat has taught me that nothing works better. I did have a sea sick prone mate for a couple years that swore by the accupressure wrist band and have heard others say it works, but I am sceptical.

Doggums tips are also good. Focus on the horizon, keep your mind occupied on something besides being sick. The stern of most powerboats will have the least motion. Sit as far back and as low as you can. Don't go in the cabin or up on the bridge. Don't drink excessively the night before and avoid a large greasy breakfast.