What is the best way to prevent sea sickness?

Many options. Staying on dry land is effective but not much fun. A scopolamine patch (transderm-scop), applied several hours before you start your trip, is effective. Wash your hands after applying. You may not be able to read while wearing it. For short trips, over-the-counter Meclizine works well. Some people swear by candied ginger or wrist bands. If you feel sick, get fresh air and look at the horizon.
Agree w Dr. Gallant. Ginger can be very effective. Auricular (ear) acupuncture with asp (acupuncture semi-permanent) needles that remain in place for up to 7 days can be quite superior to prevent sea / motion sickness. Take care.