Since you have created such interest in the Great Lakes shipping, I would like to suggest a follow-up by having you view the webcam at the locks in Soo, MI
You could tie it in nicely with your history lessons: travel, raw materials, exploration, settling communities, food, etc.
Yup, I'm a quilter and a boat nerd :-) Some large ships have been converted to barges and are moved by tugs which fit in a notch of the barge. Just another idea....