If this is an isolated sentence, I don't know what to suggest, miimi2! If the sentence is in a context, the context will tell you which one to choose. You really cannot answer the question unless you know where the passengers are (on the shore or the boat) and what they want to do (get to the shore or get on the boat)!
If you have absolutely no context, then I'd say StrangeAttitude's answer is the right one: many native speakers would assume that you were trying to get aboard before the ship before it left. This was also your first choice! So, that's what I'd go with.