Pilot Boat
A harbor pilot is a person who takes control of a seagoing ship when it is entering or leaving port. He is expertly familiar with all the channels, shoals, currents, tides, and regulations of his particular port, and is essential to safely steer the ships in and out. It is an ancient and exclusive profession, often passed down from father to son*. In old days, the top two signal flags at right were used by ships entering and exiting a harbor to call for a pilot, while the bottom flag indicated "pilot on board."
A pilot boat transports the harbor pilots to and from their charges. If you go out to the vicinity of the Ambrose Tower, you will probably see the Sandy Hook's modern descendants.
* there are very few female pilots, even today.