I learned the hard way a couple of years ago just how different the Caribbean sun is from what we have here. When I'm home, I rarely ever have to wear sun screen, and I don't burn, I just tan. I went down south and put on some sun screen, but it wasn't terribly strong - in just a few short hours, I was burned badly. I spent the rest of the vacation covered up and in the shade.
I definitely plan on spending time in the sun on the cruise, and wearing a stronger sun screen.
As much as I don't like tanning beds, I do like the fact that they decrease the chance of burning.