The boat is an entity right? It has two hearts. So an entity will turn invisible when you throw a potion of invisibility on it right. it doesn't. When you do the cheat /tp @e (username) boats don't teleport. But minecarts do. With the chest so the chests are entities to. then it should turn invisible to, it doesn't. So boats and chests and minecarts and the stuff in a minecart are entities so they should turn invisible. Ask a question it you want any more info comment.