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Polar Icebreakers in a Changing World: An Assessment of U.S. Needs
on December 21, 1936, directing the U.S. Coast Guard to assist in keeping channels and harbors open to navigation by means of icebreaking operations. Recognizing that the nations of northern Europe whose waters were often ice-covered had made major advances in icebreaking ship development in the early twentieth century, the U.S. Coast Guard directed Lt. Edward H. Thiele to make a survey of northern European icebreakers. He obtained valuable information, especially from the Swedes and the Finns. It was ironic that Thiele found that one of the most advanced Swedish icebreakers, the 258-foot YMER built in 1932, had been designed using the bow form of the Great Lakes car ferry ST. MARIE. Subsequently, Thiele was part of a team that designed a class of successful 110-foot icebreaking tugs for harbor and channel work—the first completed in 1939.
In 1941, another large icebreaking vessel was authorized and commissioned in 1942 as the STORIS. She was an enlarged 230-foot version of a class of 180-foot buoy tenders. Although STORIS was designed to serve as a light icebreaker in Greenland waters, she gained special recognition in 1957 when she, with two 180-foot tenders, became the first U.S. ship to travel the Northwest Passage from west to east.
World War II
All of the foregoing designs led to the development of the first true U.S. icebreakers, the Wind class. Once again the President of the United States was instrumental in this decision.
Rear Admiral Edward H. Thiele remembered that in 1941 he had obtained orders to the AMERICAN SAILOR as executive officer, believing that too much Washington duty might affect his career adversely. While the ship was fitted out in Baltimore, he was recalled to Coast Guard Headquarters by Engineer-in-Chief Harvey Johnson, who took him to the commandant’s office. There Commandant Waesche handed him a note that the President had written to Treasury Secretary Morganthau stating, “I want the world’s greatest icebreakers.” Thiele speculated that these ships were to support the construction of an airfield at the head of Greenland’s Sondre Stromfjord and to aid in the shipment of lend-lease supplies to Archangel, the Russian White Sea port.
Thiele, tasked to lead the design effort, was exploring various alternatives. At the same time, Secretary Morganthau recommended to the Secretary of State that the United States negotiate the purchase of one or more Russian icebreakers. The Russians offered the KRASIN built in 1917 in Great Britain. While Thiele felt KRASIN was “ancient history at best,” the deal fell through only due to the pressing need of Russia to keep the seaway to Archangel open. Thiele’s design was far different from anything ever built in the United States.
The Wind class would have half again the beam (63 feet, 6 inches), two-thirds more draft (25 feet, 9 inches), and almost four times the displacement of STORIS. Five and a half times more horsepower required two shafts, one of the most radical differences from the previous succession of single-shaft icebreaking ships, that also offered obvious advantages of redundancy in case of shaft or propeller damage far from repair facilities. The large beam let the ship cut a wide track in ice for escorted ships to follow and, as importantly, decreased the risk of ice damage to the propellers set as far inboard as possible. Similarly, the deep draft enabled the use of large propellers for strength and power, and put their blade tips deep enough to lessen contact with floating ice.
A diesel-electric propulsion plant was chosen. Proven in several previous applications, it offered economy in fuel consumption and generated relatively high horsepower for the space required. The machinery components could be arranged flexibly within the ship. The six diesel engines and generators provided redundancy and flexibility for operations that would include long periods of icebreaking at full power and lengthy, open-water transits at low power levels. Diesel-electric propulsion would also deliver maximum thrust when the ship was stopped, a frequent occurrence when operating in difficult ice conditions. Additionally, the operating environment required that machinery remain unaffected by the shocks that result from propellers striking ice, which a diesel-electric plant addresses by electrical, rather than mechanical, linkages between components.
An icebreaker’s hull form is crucial to its effectiveness. The Wind class design incorporated a sloped forefoot that met the ice at a 30-degree angle. By that time, this had become a distinguishing feature of icebreaking ships. This bow configuration, with its surface sloping down and aft below the waterline, is key to how an icebreaker works. As the ship forces itself against a horizontal ice surface, the bow rides up on the ice until the vessel’s weight breaks the ice in a downward motion and displaces the broken pieces to each side. In the Wind class design, this action distributed the icebreaking forces efficiently over the entire forebody. The stern was similarly shaped to permit backing into ice when backing and ramming.
To absorb the repeated impacts of ice and withstand its potential crushing pressures, the hull had enormous strength. Flare in the hull helped reduce frictional effects when moving through ice and in ice under heavy pressure would cause the ship to be lifted rather than crushed. The 1 1/4-inch hull plating of high-tensile steel increased to a thickness of 1 5/8 inches along the ice belt. However, the real strength lay in the entire structure of deck beams, structural bulkheads, and frames spaced 16 inches apart. Double bottoms and wing tanks surrounded the engineering spaces with a layer of protection in the event the hull plating was punctured.
The Swedish icebreaker YMER served as a general prototype for the Wind class design. The YMER influence can be seen most readily in the inclusion of heeling tanks and a bow propeller. The three pairs of heeling tanks were connected by 24-inch ducts and 60-horsepower (9hp) reversible pumps that could transfer 13,600 gallons of water per minute