You have to have a certain number of hours that you've actually spent on the water, so spend plenty of time getting hands-on experience. You can take a classroom or online course, but the information you'll cover will make a lot more sense if you're already familiar with boats. In addition to sending in a log of your hours, you'll also need to register for a TWIC card, which is a transportation worker identification card, and you'll need to pass a medical exam and take a first aid course.