The rivers surrounding New York City no longer freeze over completely –despite a lot of ice, water salinity and boat traffic keep the waterways open — but farther north on the Hudson River, in this case near Germantown, the Coast Guard’s specially-designed icebreaker boats have work to do to keep other boats moving. From The New York Times:
Breaking ice on an icebreaker boat (Two months in five minutes).
The hull has an S-shaped curve from its bow to its keel, which allows it to cut through the mounds; its weight enables it to effectively smash the ice; and its wake is perpendicular to the boat (most boats have a wake that comes out from the stern at 30 degrees), which allows for the greatest amount of ice to be broken. The Coast Guard has nine ships of this size deployed in the Northeast; there are also bigger and smaller cutters.