I haven't been seasick in years and the last time I was it was b/c I had a hangover from hell
It seems the one thing that I hear over and over is taking the medicine the night before the trip and then taking it again at least and hour BEFORE YOU GET ON THE BOAT seems to help. I have NEVER seen anyone take anything that works after they already feel queasy. The only cure at that point is sitting under an oak tree.
I've seen people eat ginger from a sushi bar, ginger ale, ginger gum etc all with some success but it's no guarantee.
Just remember, if you do get sick get to the rail and send it over the side. DO NOT go to the head, puke in the garbage can or anywhere else. The crew and fellow anglers will appreciate the courtesy.