Stupid boat trip because of parents?

So for Memorial Day my perents want to go out on a boat with two other families. Well, if we do that, that boat's capacity is over maxed by four people. I HATE BOATS and I don't want to go on the thing to start with! But my parents are forcing me to go! So yeah, I'm ticked with them right now. WTH are some things I can do to DECREASE my fear? We're going to be on the thing ALL FRICKING DAY.