Definitely do not expect to be spending a year on a cruise ship. You are going to be working hard all year, doing things you never expected to be doing. We cleaned for an hour every morning, had to fulfill Galley Duty (working in the kitchen), woke up for two hours each night for watch and then completed more watch throughout the day. It isn't an easy year, but it's the most rewarding thing you'll ever do.
When at sea, your schedule is planned out over a 5 day cycle. Each day, you will have an hour of each of your three courses (or two courses if you're a Gap year student and that's what you choose, but if you take 2 courses, you do four hours of watch per day) and two hours of watch per day. On an average day, you will wake up at 7:20, eat breakfast and then muster (or assemble) at 8. Then you will clean for an hour and at 9, the daily schedule begins. You might have two hours of watch or class, and throughout the day you'll have breaks. At 11:30 there's lunch and then classes start up again at 13:00.
A snack is provided at 15:00. At 18:00, you muster again and then your day is done, unless you have watch from 18-20:00 hours. Dinner is at 18:30, and then there's study hall from 19:00-20:00, which is when your teachers are available to answer questions or you have time to do homework. Afterwards, there is sometimes an activity planned such as a movie showing or a talent show. The five day cycle keeps going until you hit land, where you will have shore leave and get to explore each port. There's no school when you're in port, which is why you don't have "weekends" out at sea.
I think I was most afraid of losing a year of school back home. It didn't take long before I realized that there was so much more to life than following a conventional schooling pattern. In the adventures I was living every day and the cultures I got to delve into, my anxiety over my education quickly dissipated.