Loud horn at 11:40pm every night - what is it (sounds like a ship)?

I live near Flatbush and Park Place and over the years have heard what sounds to be the horn of a large ship at night coming from the distant northeast. I have recently established that it goes off at 11:40pm each night -- well, at least it did this past Saturday and Sunday, when I started tracking the time. Does anyone know what it is?

There's been speculation about this discussed on various boards over the years. Haven't seen a 100% sure answer. The most plausible one might be someone saying confidently its the staten island ferry. when weather / wind conditions are right, the sound can carry. But I've only heard it at night myself, so seems to disprove the ferry idea.

I used to hear something similar when I was at 7th Ave and Carroll, years ago. Thought at the time that maybe it was a boat captain asking for one of the Gowanus Canal bridges to be raised. But that's not to the NE and that 11:40 pm seems a bit late.

i've heard ships from here for years, usually at night because it's quieter then.

Yes, we hear it too, on quiet nights here on Vanderbilt and Prospect....sounds to me like a ship's horn in the East River.

I have always wondered if others thought the same thing when hearing the ship horn - thank you for starting the thread!

Years ago I had a roommate who was a transportation reporter for the Staten Island Advance. According to a conversation a 10 years ago, it's the Staten Island ferry.

I used to live near a business district and had a similar problem at a similar hour of night. My theory was that it was a private carting company / garbage truck and that the driver was using his horn for "signalling" to the staff that was hanging off the back of the truck.

good luck.