Tuesday, September 23, 2014

1905,1930 Aerial Lift Bridge over the 1870 Duluth Ship Canal

(The original contents of this post has been moved to Frankfort, IN.)


A video of Paul R. Tregurtha having to do an emergency 360-degree turn because of issues with lifting the span of this bridge was my motivation for finally documenting this bridge. I've seen plenty of YouTube videos of boats passing under the bridge because the boats and the bridge tender generally "salute" each other. Saluting is sounding their horn.

In the above video, you can see the prop wash of the main propeller, but I could not see any prop wash for a bow thruster. The following photo confirms it has a bow thruster marking. So was it able to do that tight turn with just its rudder? That would explain why it maintained power and speed during the turn.

Interlake Steamship Company posted
Hello Twin Ports! Our M/V Paul R. Tregurtha sails under the iconic Duluth Aerial Lift Bridge on her way to Superior to take on more than 60,000 tons of coal. It will take her 2.5 to 3 days to transport the essential cargo to the DTE power plant in St. Clair. #shippingmatters
📸: David Schauer

Damian Entwistle Flickr, cropped; License: Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0)
Duluth - Enger Tower, view to lift bridge

Damian Entwistle Video, cropped; License: Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0)
Duluth - Enger Tower, lift bridge and laker

The reason for the two dates is that it was originally built in 1905 as the transporter shown in this photo. In 1930, after raising the transporter truss and reinforcing the towers, a lift span was added.
Tom Wigley Flickr, License: Attribution-NonCommercial-ShareAlike 2.0 Generic (CC BY-NC-SA 2.0)

Aerial bridge. Duluth, Minnesota

Circa 1905. "Aerial bridge. Duluth, Minnesota." Suspended Car Transfer over the Duluth Ship Canal. The gondola could carry 60 tons of cargo across the 300-foot channel with minimal obstruction of the shipping lane. After modification for service as a vertical lift, the span became known as the Aerial Lift Bridge. 8x10 dry plate glass negative, Detroit Publishing Company.


HAER MINN,69-DULU,9--4, cropped
4. SOUTH ELEVATION OF BRIDGE, WITH THE 'ROGER BLOUGH' HAVING PASSED UNDER - Duluth Aerial Lift Bridge, Lake Avenue, across Duluth Ship Canal, Duluth, St. Louis County, MN

The bridge spans the Duluth Ship Canal, which was dug in 1870 through the sand bar that routed the Saint Louise River further south and east before opening into the lake. The sand spit, commonly called "Park Point" by locals, named Minnesota Point, allowed ships to avoid Superior WI while still getting from the river to Lake Superior. This also turned the peninsula into an island. Ferries worked - but not during icy winter. 
In 1892, John Low Waddell designed a high lifting vertical lift bridge. The War department did not approve so Duluth did not get to build it. But the design was modified and built in Chicago as the South Halsted Street Bridge. Thomas McGilvray, a city engineer, drew the plans for the structure that was built, apparently inspired by a similar traveler type bridge, the Rouen Transporter Bridge across the Seine.

By the late 1920, the bridge was not keeping up with demand. The upgrade began in 1929, adding lifting span with a automotive deck. The fix span across the top had to be raised to allow room for the lifted span, so the towers straight vertical sections were added. In addition, significant structure was added within the towers to accommodate the counterweights and lifting mechanism. The rebuilt bridge first lifted for a vessel 1930 Mar 29.

[Bridge Hunter Description]
So was the War Department afraid that the lift span would fall down?

LC-USF34-064038-D (b&w film neg.), cropped
Aerial bridge. Duluth, Minnesota

LC-USF34-064039-D (b&w film neg.)
Aerial bridge. Duluth, Minnesota
[Note that the ship has passed and the lift span is on its way down.]

LC-HS503- 705
Credit line: Photographs in the Carol M. Highsmith Archive, Library of Congress, Prints and Photographs Division.
Carol M. Highsmith's photographs are in the public domain.

Al Miller posted three photos with the comment:
Edgar B. Speer departs Duluth in late March 1984 as the first boat to leave port that spring. She's bound for Two Harbors to load taconite pellets. G-Tug Vermont will accompany the Speer to assist with icebreaking and docking.
I was working for the Duluth News-Tribune at the time and had just done a story previewing the shipping season -- always one of the most pleasant tasks of the year. The photographer assigned to shoot the first boat movement persuaded me to accompany him -- probably so he wouldn't have to write the two-sentence photo cutline himself. He knew the operators of the Aerial Bridge, so we were able to be on the span when they raised it to allow the Speer to pass. I don't remember why I had my camera with me that day, but I'm glad I did. I wasn't a big fan of the 1,000-footers but this turned out to be a series of photos I still treasure.
1

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3

 

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