What is the longest running ferry boat or ship in maritime history?

The MV Commander is the longest continual service ferry boat in current operation. Im unsure if it is the longest all time though.

I can't say if its the longest in history, but the SS St. Mary's Challenger has been in service for over 100 years (mostly as a cement carrier). And since ships tend to last much longer on the Great Lakes because of the fresh water, I'd think she could possibly be the longest serving overall. More info can be found on the boatnerd website boatnerd.com

The oldest licensed passenger crossing runs across the Thames in England from the town of Hampton to Molesey Hurst. The earliest known record of ferry operation here was in 1514 making it about 500 years old. The Hampton Ferry has not used the same boat for this length of time though so it is not the oldest ferry boat, yet it does remain the oldest licensed crossing...still an impressive feat for such a humble ferry.