I, thankfully, never suffered from motion sickness even in really big seas. The below is actually fairly calm seas:
The keys for me were:
- Eat. Saltines were mentioned.
- Patch. Get the prescription stuff. I never needed one but they do work.
- Stay on the bridge. If possible, stay above decks. The closet I ever came to getting sick was during the monsoon season in the Indian Ocean. Huge seas, Perfect Storm seas: For days. 75% of the crew of the Frigate I was on were sick. Some guys were on IV's. I got my lawn chair out when I felt bad, sat against the hangar doors on the flight deck and tied myself in. Watched the horizon and instantly felt better.
- Go on a one day something trip before the ten day. The tuna boat is going to move, a bunch.
This is a good link:
Avoiding Seasickness - Cruises - Cruise Critic