• Short Summary

    The world's largest mobile offshore rig went to sea today -- after some tricky manoeuvring to duck under San Francisco's Golden Gate Bridge and jump over a sand bar at the mouth of the bay.

  • Description

    The world's largest mobile offshore rig went to sea today -- after some tricky manoeuvring to duck under San Francisco's Golden Gate Bridge and jump over a sand bar at the mouth of the bay.

    With its four "legs" towering 200 feet above water, the 4500-ton "George F. Ferris" headed toward Los Angeles, where it will soon begin "walking" the ocean floor to assemble the largest, heaviest, longest and deepest pipe ever pieced together underwater.

    Named after the president of Raymond International Inc., sponsor of the contractor combine building the record size pipe, the unique rig was too tall to make a simple exit from San Francisco Bay, where it was built. Its 275-foot legs were first jacked down to clear the bridge's 232-foot high deck, and then jacked back up to clear the sand bar.

    It will take about five days to reach the shores of El Segundo, where it will jack down its legs on to the ocean floor and begin laying first sections of the five-mile long sewer pipe line. Large enough to accommodate two men, one standing on top of the other, the 12-foot diameter pipe weighs almost four tons per linear foot.

    The $20 million sewer job is being handled by Hyperion Constructors, a joint venture of six well-known construction firms. They are the DeLong Corp., New York; Healy Tibbits Construction Co., San Francisco; Peter Kiewit Sons' Co., Omaha; Macco Corp., Paramount, Calif.; Raymond International Inc. (formerly Raymond Concrete Pile Co.), New York; and Tavares Construction Co., La Jolla, Calif. The contract is with the Board of Public Works, City of Los Angeles.

    Erecting the 275-foot legs at a deep water dock in San Francisco Bay was a major problem in itself. Swift tides actually broke the craft loose from its moorings one night and it drifted a half mile before it was retrieved.

    But the real problem was getting the mammoth tower out of San Francisco Bay. Its four 275-foot legs first had to be jacked down to clear the 232-foot high deck of the Golden Gate Bridge. Then, just after it passed the bridge, the "George F. Ferris" was anchored for a few hours while its legs were jacked back up. With the lower 40 feet of each leg protruding underneath the hull for stability, it passed over the shallow bar at high tide and went to sea. High tide was a requisite for clearing the sand bar.

    Function of the "George F. Ferries" is unique. It will lower assembled sections of pipe to the ocean floor, connect with previously laid sections, and the backfill around then with a cradle of gravel. After each 192-foot long pipe section weighing approximately 600 tons is laid, the rig "walks" ahead by first jacking down its platform on the legs until the entire unit is floating. Then it winches itself ahead to the next pipe position, lowers its legs and lifts itself above the reach of waves to repeat the unusual pipe laying sequence.

    The self-elevating principle, developed by the DeLong Corp., has been used to install offshore oil drilling platforms and also the first Texas Tower radar station in the Atlantic Ocean. But the technique has never been attempted at such a great depth of water, or on a device requiring so many separate jacking operations. To lay the 32,000 feet of offshore pipe, the "George F. Ferris" will be jacked up and down at least 170 times. Pipe alignment, jointing and backfilling will be carried out under the watchful eye of closed-circuit underwater television.

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    Reuters - Source to be Verified
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    Available on request
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