How can one prevent seasickness?

Alternative options. Dr tosca gave an excellent response. Here are alternative options: acupressure, sea-bands and ginger or peppermint tea.
Dramamine (dimenhydrinate) U can use dramamine (dimenhydrinate) otc (over the counter). A more effective medication is scopolamine patch (prescription). These help for the sea sickness feeling. It may help for vomiting. But generally different prescription medications r better for vomiting (ex.Promethazine). The most important thing w/ vomiting is dehydration. In other words you don't anything as long as u can maintain hydration.