Transderm-Scop
"I was on small military ships for 5 yrs. Used Transderm Scop ALOT. By far, it's the most effective seasickness medicine that I encountered; I tried a great deal of those other medicines. With all powerful meds, however, come serious side effects. The worst is that it made me feel generally weird and depressed - I cringe when I think of putting a patch on. It gave me dry mouth and a bad after-taste. Lastly, it blurred my vision slightly. 

IF you time it right (put it on 4 hr before the heavy seas), you'll be seasick free. If you DON'T time it right (such as you exceed the 4 hr window b/c the heavy seas don't come rt away), you'll still have positive results, though not as effective. With it, I could concentrate and work well in any sea state."