Ginger helps, carry some crystallized ginger or ginger flavored hard candy if you can find it. But sometimes you just have to take that pill! Or, how about a patch that sticks behind your ear? Are you taking a cruise? Watch the weather, if it is calm at first you shouldn't have any trouble, but if high seas are predicted a pill is better than misery.
Are you troubled by carsickness? If not then you will probably find your sea legs pretty quickly.