[Eric in the Ozarks]

There are estimates but a real number isn't known. Steel vessels last almost indefinitely in cold fresh water.
The steamer E. M. Ford was built in 1898 and is still in service for Inland Lakes Transportation Co of Alpina, Michigan, hauling cement. Like a lot of these old girls, she was cut in half and lengthened and her coal stoker system replaced with Number 6 oil many years ago.

[markman46]

thanks, guess I am going to have to make a trip back to Duluth and stand under the lift bridge, and check out the ships coming and going.