How can I get over my fear of boats?

I am going to Catalina Island soon with my friend and her family, and I REALLY want to go; sounds like a great offer since they’re paying for it and it’ll give me something fun to do over my summer break. However in order to get there we have to take a large boat, and I’ve always been kinda terrified of big oceans and boats. What can I do to get over this fear? Thanks!!