A lot of coal that moves on the Ohio River comes from docks on the tributaries. In my part of the river, that means the Kanawha and the Big Sandy.
Here's the Donna York bringing 12 barges out of the Kanawha on a fine afternoon.
You might be able to notice the barges are loaded to 10 feet. From what I've seen, 9 feet used to be the norm. Now it's 10 feet. On a jumbo barge, that extra foot is worth about 200 tons.
That's because a barge is 195 to 200 feet long. Let's go with 195 here. The barge is 35 feet wide. Each foot of depth displaces 6,825 cubic feet of water. One cubic foot of water weighs slightly less than 62.43 pounds. Thus, every foot on a coal barge displaces about 426,085 pounds of water, or about 213 tons.
So, those 12 barges pushed by the Donna York were hauling about 2,556 tons more at 10 feet than they would have at 9 feet.
Did I get all that right?