Following Prince Caspian much more closely than it in turn followed The Lion, the Witch and the Wardrobe, The Voyage of the Dawn Treader follows King Caspian along with Edmund, Lucy, and new character cousin Eustance as they set out on a great voyage across the sea to find a series of Lords exiled before Caspian took the throne.
After that, the entire book basically takes the form of a series of smaller adventures, each taking a chapter or two. It reminds me a lot of Ulysses; perhaps that’s the boat connection. Each of the stories is actually pretty good (my daughter and I both particularly enjoyed the Dufflepuds. They’re just silly enough for her age group. That being said, it’s weird that the King can do something like that (leaving his kindom, potentially for years) and it means that the story doesn’t have much of an overarching plot, but it works well enough.