A trip across the widest part of the Hudson River from Haverstraw, New York to the Ossining, New York MetroNorth train station. At the train station in Ossining, you can catch a train into Grand Central Terminal in midtown Manhattan or points north. The whole trip to Grand Central, including the ferry ride, takes about 1 hour.
It is possible to work in Rockland County and use the ferry to get there from Westchester, NYC, or points north. Check the ferry schedule, which conveniently lists reverse directions and when the ferry departs or arrives at Ossining or Haverstraw. More and more commuters are using the ferry to “reverse commute.” The ferry can also be used to get to White Plains, believe it or not. Once you arrive in Ossining, wait for the 11, 13, or 14 Bee Line Bus directly to White Plains: map here.
HaverstrawLife.com 
Let me clarify: this is a “reverse commute” because I took the ferry in the evening, back into the City. The commuting crowds are normally flowing in the opposite direction at this time, however, a few people did join me on this ride. The Haverstraw Ferry is a viable way to commute in reverse from New York City to Haverstraw.
I’ve been seeing various searches to the site asking if the ferry runs on weekends. The ferry does not currently run on Saturday or Sunday. The ferry is intended for commuters (Mon – Fri), although some people use the ferry to come up to the Hudson Valley from the New York City area for the weekend, or overnight.