Page:Popular Science Monthly Volume 90.djvu/901

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Popular Science Monthly


��Francisco for less than $29,000. Her original cost was 8210,438.00.

Mr. Hooper is a lumberman and not an engineer. Nevertheless, it was he who devised a plan for raising her. From photo- graphs of her, maps and other data, he decided that if all the shell holes were stopped, if her sides were ex- tended upward until they pro- truded out of the water, and if the water were then pumped out of her hold and out of the extension top, she would rise of her own accord. Why? Because the volume of water displaced by the extension form outweighed the force tending to buoy her up, and when removed left no alternative but for the vessel to float. The form, or cofferdam, as that kind of structure is known, was built to displace 4,500 tons of water.

There was assembled in San Francisco and sent to Papeete the material for a wooden cofferdam 307 feet by 14 feet in height forward and 32 feet aft, plus an additional 25-foot section in the form of a V and also 32 feet high, to encompass the stern. The material assembled included some 600 tons of tongue-and-groove planks, beams and joists, 13 tons of structural iron, chains, hangers, pipes, etc., four direct connected centrifugal pumps, one double-

���The Walkure rose to the surface like a cork as the water was pumped out of the cofferdam

��action Worthington pump and two pul- someters.

Divers were sent down to patch up the Walkure. Then the first 18-foot section of the cofferdam, constructed on shore, was lowered into place. The coft'erdam was

constructed of 2-, 3- and 4-in. planks, the thick- ness increasing with the depth of immersion. These were bolted and nailed to the joists, the entire construction re- sembling a huge water-tight rec- tangular box with- out top or bottom. Resistance against t he exte- rior crushing force was secured by use of transverse beams 14 by 14 in., reinforced by longi- tudinal supports 6x8 and 8 x 10 in., tying together the different sections.

Next the water was pumped out. When the vessel floated a little she was towed a little nearer shore. The first movement of 125 feet was followed by a second of 146 feet on the following day. Pumping was then stopped and five days spent in sawing away the elevated portions of the cofferdam in order to provide stability and remove weight and topheaviness. One day later the vessel was afloat on her own bottom and the process of cleaning up was begun.

Four weeks were spent in getting the

���One of the shell holes made in the Walkiire's hull after she was captured by the French

��How the big shell hole shown at the left was plugged up before the pumping began

�� �