Hi Steve,
I've been to NY a few times on business and like Gordon says above, not much in the way of shipping although I found the cruise terminal on the west side (Hudson River) busy at weekends with three or four ships sailing each day around about 4:30pm, all sailing one after the other. The South Street Maritime Museum is also worth visiting on the east side (East River). I found the Circle Line excursion quite interesting seeing the above plus any passing tug/barge traffic and local ferries. They run from the west side just south of the Cruise Terminal and you also get a good view of most of the NY attactions.
The free Staten Island ferry gives views of the anchorages in NY bay plus Staten Island gives a good view af all commercial traffic in & out of the ports in New Jersey. The crossing also gives good views of the Statue of Liberty.
The USS INTREPID museum is/was worth a visit but I believe she has been moved for restoration work.
If you get mobile then a trip down to Bayonne (by the Bayonne Bridge) is worth a trip to seen ships moored on the Jersey container port and any passing traffic.
Have a good trip.
Bob