General Dynamics Building Cargo Transfer Platform Barge With National Jacking System

An offshore jacking system built by National Supply Company, Houston, will give "legs" to a cargo handling barge designed for shipping major marine components between New England shipyards.

The jacking system will enable General Dynamics' Electric Boat Division to load and unload components at dock level, then raise the legs and tow the barge between its shipyards in Groton and 50 miles up the coast at Q u o n - set Point, R.I.

Also described as a "cargo elevating platform," the barge will be 195-feet long and 78- feet wide with a capacity of about 1,200 tons.

The barge is expected to make about 25 trips a year between the two shipyards with components weighing up to 600 tons.

National's jacking system was developed for the offshore oil industry. Drilling or production platforms fitted with the jacking system could be towed to an offshore oil field. Then the legs would be jacked into place to create a stable platform in varying water depths. The legs could then be easily retracted whenever the platforms needed to be towed to a new location.

Bruce Dawson, sales engineer for National's Drilling Equipment Division, Houston, said the rack-and-pinion jacking system consists of three independent jacking units and legs. Each cylindrical leg, fitted with a sawtooth rack, is 72 feet in length, with an outside diameter of six feet.

"The system is electrically controlled and can be powered from shore-supplied power sources," added Mr. Dawson. "The electrical system provides smooth and continuous movement for the precise adjustment of the platform to the docks in a minimum amount of time." The barge loading and jacking system idea grew out of a brainstorming session at Gen- eral Dynamics. Cranes used in recent years had been limited to 300 tons and the Electric Boat Division sometimes wanted to transport far larger components.

The jacking units were manufactured at National Supply Company's plant in Torrance, Calif., and the legs and racks were made in Houston. The equipment was then shipped to Quincy, Mass., where the barge is being constructed by General Dynamics' Quincy Shipbuilding Division.

National said the barge jacking system should find an easier service life than those used on many offshore installations.

"We're really looking at an ideal situation here because loading and unloading will be done in protected areas on concrete pylons and under good weather conditions," he said. By comparison, some offshore jacking system legs used on drilling rigs are longer than a football field and are expected to withstand severe pounding from ocean waves and high winds.

Mr. Dawson said jacking systems can be used for other non-oilfield purposes—such as portable drydocks, bridge erection and pile driving.

For free literature on National Supply's offshore jacking system, Write 9 4 on Reader Service Card

Maritime Reporter Magazine, page 54,  Oct 15, 1983 Maryland

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