Sounds like a ship's horn?

Subject: Sounds like a ship's horn?

I live in the North Slope near Prospect Park, and every once in a while I hear what sounds like a distant ship horn. We're too far from Red Hook to hear the cruise ships, right? Sometimes I hear the noise as late as around 10pm, which I assume is too late for the ships anyway, right?
Any idea what such a noise could be if it isn't a ship?
My wondering started as mild curiosity, but now I really want to know.

It's a ship's horn - tug boats, most likely.

agreed. if the wind is blowing the right way, sounds carries pretty far!

Staten Island Ferry.
Hear it all the time, since the ferry runs 24 hours.

Subject: after hours

i think most ships now have an 11pm curfew.