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March 24, 1905: Several test trips determine the new Aerial Transfer Bridge can handle a load

On this day in Duluth in 1905, workers employed by Milwaukee’s Modern Structural Steel—builders of Duluth’s aerial transfer bridge—tested the gondola car to see if it was capable of carrying the weight specified by its designer, C.A.P. Turner. The ferry car itself would be fifty feet long and over thirty feet wide, with a seventeen-foot-wide center roadway and seven-foot-wide walkways on either side. The middle thirty feet of each walk would be enclosed to form a cabin. Cables powered by two fifty-horsepower electric streetcar motors installed beneath the ferry (only one would operate at a time, the other reserved as a back-up) would drive the ferry car at a rate of four miles an hour. The motors turned a drum on the side of the car; the cables wound around the drum and up to a traveling pulley—a truck holding many sets of wheels, really—that rode along the truss. The revolving drum set the car in motion. If the electric motors failed for any reason, operators could use a hand gear to move the car safely to shore and out of the way of oncoming vessels. When at rest, the ferry car would hang over dry land, allowing ships to pass freely. Turner proportioned the gondola car to carry a loaded streetcar of 21 tons with the remainder of the floor loaded with 110 pounds per square foot—about 65 tons. So MSS workmen loaded the ferry car with sixty-five tons of steel rails, reels of phone wire, cable, a steam boiler, and heavy timber, “greater than any load that the bridge is likely to be called on to carry, at least until street cars are taken across.” Even under all that weight, the bridge operated smoothly, crossing the canal six times. The newspapers reported that the bridge would likely never have to carry such a load, as its capacity was for 600 passengers, estimated to weigh 39 tons. Sunday, April 8, was the first real busy day for the bridge. Engineers counted 32,595 people boarding the car in one 12-hour and 20-minute span. One trip at 3:30 p.m. that Sunday took 814 passengers—an estimated 55 tons of human cargo—and 214 passengers over the limit.

Duluth’s Aerial Transfer Bridge’s gondola car ca. 1907. (Image: Lake Superior Maritime Collection)