Translation:The boat is full of nice tourists.
Da joins two nouns - the container and the contained. So I think it's boato da turistoj, but boato plena de turistoj. (The Wikipedia Esperanto grammar article says da "is semantically Slavic and is difficult for Western Europeans, to the extent that even many Esperanto dictionaries and grammars define it incorrectly," and then links to this very useful Wiktionary article on da: https://en.wiktionary.org/wiki/da#Esperanto
It's simple: If somebody who knows what they're talking about calls it a ship, it's a ship. Likewise, if somebody who knows what they're talking about calls it a boat, it's a boat.
Despite all the rules of thumb that you may hear, the real answer is that traditions determine when to use boat or ship, and traditions have little respect for rules.