Well, in italian you have "nave" and "barca" in order of size, the second one being just a little boat you can use, say, to go fishing. I'm not a native English speaker, and even though I think a boat would be smaller than a ship, I've seen "boat" being used for what in Italian I'd call "una nave". So, I think "boat" should be accepted.
In the British nautical tradition, you can carry boats on ships but not ships on boats. It pains a sailor to hear "boat" being used when it's really a "ship". Sadly these days journalists don't make the distinction and Americans always refer to a 50 thousand ton vessel as a "boat"!