Bellingham to Skagway is 70 hours 15 minutes scheduled. Not sure if it really counts because there are intermediate stops at Ketchikan, Wrangell, Petersburg, Juneau and Haines. Since we are talking RORO, the vehicle never leaves the ferry if loading was done correctly.
http://www.dot.state.ak.us/amhs/docu...r09/SE_W09.pdf