Closer view of such boats
As to the height of vessels, it is to be noted that the great bulk of navigation under the bridges is not through traffic, but is simply movements about in the lower stretch of the river which forms part of the harbor of Pittsburgh. The commodities moved are nearly all sand, gravel and coal in barges, which loads are almost invariably taken up stream while the downward movement is mostly of empty barges. These barges are mostly moved by harbor tugs. The harbor tugs actually in use are from 22 to 27 feet high, averaging about 24 feet.
Allegheny River heights for each day, 1906-1907.—U. S. Engineers' Report (Diagram 5)
Allegheny River heights for each day, 1908-1909.—U. S. Engineers' Report (Diagram 5)
The heights of the Monongahela standard towboats vary from 24 to 32 feet, averaging about 28 feet. Out of a list of 28 such boats but 5 exceed 28 feet in height.