Other Failure Cases/Liberty Ship
Liberty Ship Fatigue Failures
The Liberty Ships of World War II were an engineering and industrial solution to a specific military and political problem. The problem was that is was necessary to build merchant ships faster than the German Navy submarines could sink them, in order to supply the United Kingdom and sustain its war effort. The problem was complicated by the fact that the Great Depression had greatly reduced U.S. shipbuilding capacity.
Between 1930 and 1937, U.S. shipyards built only 71 merchant ships. However, 5,777 were built between 1939 and 1945. This was made possible by changes to construction methods, as well as the standardized Liberty freighter and similar T2 tanker designs. One shipyard built a Liberty ship in five days. The massive increase in production was possible in large part because of a change from riveted to electric-arc welded construction. Shipyards were organized for maximum efficiency around the welding process. New welding equipment was developed for heavy steel ship plate. The German pocket battleships had pointed out the efficiencies of welded ship hulls. By saving a thousand tons of weight in the hull, they could carry that much more armament (Tassava 2003, pp. 90 – 93).
One of the best known Liberty Ship failures was the S.S. Schenectady.
“At 10:30 pm on January 16, 1943, an explosive boom shattered the cold night that had settled over the Swan Island shipyard outside Portland , Oregon . Rushing to the fitting-out docks where the yard’s T2 tanker vessels were completed, graveyard shift workers discovered that the yard’s very first ship, the S.S. Schenectady, had cracked in half amidships (see Figure 1). The ship’s deck and side shells had fractured completely; only the plates running along the bottom of the [162 m] 532-foot long hull held the fore and aft sections together.” (Tassava 2003, p. 87).
Although this wasn’t the first cargo ship failure, it was highly visible, as the first ship built in the new yard. In March, another tanker, the Esso Manhattan, split in half while entering New York harbor. In January 1943, about 20 ship failures occurred, with 4 or 5 suffering Class I damage or total hull failure like the Schenectady . Twenty Class I failures occurred in January 1944, with 120 failures in the following March. Many failures occurred in the open ocean. Since the Schenectady and Esso Manhattan failures occurred in port, the ships could be put in drydock, repaired, and put back into service (Tassava 2003, pp. 88 – 90).
The solutions fell into three categories – improvements to shipyard practice, retrofits of the completed ships, and changes to the design. Two different anti-fracture design changes were made. The first was to redraw the Liberty ship plans to round off the troublesome hatch corners. The second was to install crack-arresting devices, to stop cracks from propagating through the hulls. It had been observed that fractures were generally stopped by perpendicular barriers such as riveted or especially strong seams (Tassava 2003, p. 101). In the early Class I failures, such as the Schenectady and Esso Manhattan, the cracks had been able to travel completely through the hull.
The gunwale bars and the other retrofits were successful. No ship with gunwale bars ever failed in service. Through the end of the war, only 127 of the 4,694 Liberty ships and T2 tankers ever suffered a Class I fracture, and no ships with anti-fracture devices failed. Two years after the war “an official board of investigation determined that faulty workmanship caused exactly 25 % of the 2,504 fractures which had occurred up to August 1, 1945, that a combination of inferior workmanship and inadequate design caused another 20 %, and design so poor that ‘perfect workmanship would have done little to prevent the failures’ caused a stunning 55 %” (Tassava 2003, p. 103).
The complete case study is provided in Chapter 9 of Beyond Failure: Forensic Case Studies for Civil Engineers. A useful review of the Liberty Ships as well as the problems and solutions of welding was written by Christopher James Tassava, “Weak Seams: Controversy over Welding Theory and Practice in American Shipyards, 1938 – 1946,” History and Technology, Vol. 19 No. 2, pp. 87 – 108 (Tassava 2003). Tassava is a historian, not an engineer, but does a good job of reviewing the technical issues associated with the failures. This case study is featured on the History Channel Modern Marvels More Engineering Disasters videotape/DVD. However, the History Channel version seems oversimplified.