i do not know of any shots available for sea sickness...there are shots available for vomitting, like phenergan or zofran. But i'm betting if you go to the ships Dr with those symptoms you might find yourself quarantened for fear of norwalk virus...just a guess tho.
You could visit a Dr here in the states to get the patch before sailing. I'm thinking an urgent care clinic might help you but i'd call one first and make an appt after asking if they would perscribe it.
Just a note...i'm unfortunatly going to say, that perhaps if you get this sick on cruise ships maybe cruising isnt the best vacation for you. I know if i was sick that badly i wouldnt enjoy myself enough to spend my vacation money and time on it. Perhaps you'd be happier in a resort, and flying? Good luck.