Hi CruisingUK...we are coming in from RI which is about a 3.5 hour trip and we wondered the same thing about getting to the ship. I found this website that addresses to ways of getting there. Maybe this will help you? http://www.cruiseliberty.com/dirpark.htm
Scroll to the bottom where is says "Public Transportation" which will give you by train and by bus directions.
We are contemplating staying the night before as well but then also thought it might be nice to extend our vacation the night we get back to NYC on the 27th...something to look forward to when we are sad our cruise is over!