The ore jenny, sometimes referred to simply as an ore car, was born largely out of need to more efficiently maximize a hopper's space. This particular product could just as easily be hauled in the standard hopper normally assigned in coal service. However, because ore is so much more dense a hopper can only be partially filled before its weight limit is reached. In some cases railroads continued to move ore in this fashion, even through the postwar period, providing the odd scene of a "loaded" 50 or 75-ton hopper only half full. The jenny solved this problem as it was much shorter, in both length and height, than its larger cousin but was otherwise identical in operation featuring bottom-fed chutes (usually one or two) in which ore could quickly be unloaded.
While it is unknown exactly when the first jennies entered service it is believed they began appearing during the mid-19th century when the first iron mines entered production. At that time mining operations were scattered across the east and found in states ranging from North Carolina to the Northeast. Unfortunately, most of these provided a rather low-grade ore that was not particularly profitable. Of course, everything changed when vast amounts of high-grade iron were discovered in Michigan's Upper Peninsula and northern Wisconsin during the 1840s and 1850s as well as parts of Minnesota between 1866 and 1904, according to the U.S. Geological Survey. Most mining operations here began appearing after 1870, coinciding with the widespread use of the ore jenny, which was also around the time the American steel industry blossomed.
Iron is a key component in the production of steel and railroads were poised to reap the profits from moving this commodity to new mills in places such as Pittsburgh, parts of Ohio, and the Upper Ohio Valley. The first ore jennies were rather small designs and as Patrick Dorin points out in his book, "An Illustrated Guide To American Freight Train Equipment," since they were constructed primarily of wood could only handle about 30 tons of product. As iron and steel became widely used in car construction during the early 1900s jennies, along with most other freight equipment, grew in size to 50 tons, 70 tons, and eventually 75 tons. Today, the car hauls anywhere between 85 to 100 tons and newer models are nearly identical in appearance to standard hoppers only slightly smaller in length.
To understand just how dense ore is in comparison to coal or aggregates a jenny built during the postwar period was around 24 feet in length (measured coupler to coupler) with a capacity, as previously mentioned, between 50 to 75 tons. By comparison, a hopper carrying the same tonnage was much longer, usually between 40 to 50 feet. Mr. Dorin goes on to note that the 24-foot design became an industry standard since the car fit quite well on an ore dock which utilized dumping pockets (used to load water-going freighters) that were 12 feet in length. If the train of jennies was placed just right, every other car could be spotted for unloading. Once these initial pockets were filled the entire consist was shifted to load the remaining unfilled pockets. While it may not appear so it was actually a very efficient operation.
Today, such ore docks can still be found in service but new operations often utilize car dumpers instead. During the iron industry's peak years most railroads serving the Upper Midwest all operated their own docks along the Great Lakes such as the Great Northern at Superior, Wisconsin; Milwaukee Road and Chicago & North Western at Escanaba, Michigan; Wisconsin Central/Soo Line at Ashland, Wisconsin; and the Duluth, Missabe & Iron Range at Duluth, Minnesota. Additionally, there were numerous ore docks located in the state of Ohio at locations such as Cleveland, Huron, Toledo, Lorain, Ashtabula, and Conneaut operated by railroads like the Pennsylvania, Bessemer & Lake Erie, Wheeling & Lake Erie, New York Central, and Baltimore & Ohio for transporting iron to steel mills located in West Virginia, Ohio, and Pennsylvania.
With the United States steel industry a mere shell today of what it was only 30 to 40 years ago the need for iron, and ore jennies to transport it, has dropped dramatically. However, loads of taconite still roll over the nation's rails and can be found in service on BNSF and Canadian National (after the latter acquired DM&IR in 2004). You can also find ore moving over CSX and Norfolk Southern. Despite the great decrease in production over the years, as long as portions of the Upper Midwest continue to provide rich seams of iron there will most likely always remain at least a few ore jennies rolling along in service around the country.
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