Wife Judy gets seasick and has tried many things. Here are her comments. The Scopolamine patch works well for many people, but it spaces Judy out completely, so she doesn't use it. Instead, she deals with potential seasickness by taking a prophylactic (preventive--ahead of time) daily dose of meclazine, which is sold as Bonine. She takes her first dose about noon on day of embarkation and then 1/day every day. She also brings sea-bands for her wrists, but has never used them on the blues cruise, which is a testimony to the stability of the big ship. She drinks with vigor, and that's not a problem with Bonine, but don't know about Scopolamine. With either Bonine or Scopolamine, the sooner you get the drug in your system the more effective it will be.
The HAL ships are very very stable. The Eurodam, being almost brand-new has the most modern stabilizers available, and they really do work to make the ride less nauseating. You may discover that you don't have a problem at all, but it never hurts to be prepared.