Installation of the three Cognac Jacket sections using eight winches and two derrick barges required an extensive array of electronic instrumentation and hydraulic controls. A brief description of the electrical subsystems is presented with some comments on experience. Major items included are winch control and jacket monitoring telemetry, acoustic positioning, trainer/simulator, subsea cameras, and communications systems.
The decision to build Cognan in three sections created several requirements not previously required for platform installation. Of major significance are the following:
A ballasting system for precisely flooding the floating jackets to weigh 800,000 lbs. in water.
A leak detection and deballast system to allow quick reaction to accidental jacket leaks.
A winch system large enough to lower a l4,000-ton jacket, ballasted to 400 tons, over 1000' to the ocean floor.
A barge positioning and mooring system capable of maneuvering the suspended jackets for underwater mating (must hit an 8-foot target with a 2-foot pole).
A jacket leveling system capable of leveling the jacket to 0.15° of level (3 inches per 100').
A pile handling system capable of stabbing, driving and grouting 24 piles (84" by 615 ft. long, weighing 500 tons) into a 96" sleeve in 900' of water.
An environmental monitoring system to measure wind and current profiles during jacket and pile installation.
A centralized supervision and communications center to control all operations.
This paper briefly describes some of instrumentation subsystems used to monitor and control the above systems.
Initial design of the above systems for the Lower or Jacket Base Section (JBS) installation started in January 1976. Selection of all contractors was completed by September 1976 and all equipment was operational on the JBS and derrick barges by July 1977. Installation of the JBS and piles was completed in early October 1977.
Design of the Jacket Middle Section (JMS) and the Jacket Top Section (JTS) instrumentation began in June 1977. Contractors were selected by September 1977 and all equipment was operationable by June 1978. Installation of the JMS, JTS and leg pins was complete by October 1978.
Monitoring and control of the Cognac instrumentation system was centralized in two buildings (Fig.l), one on the primary Derrick Barge No. 16 (DB 16) and one on the secondary Derrick Barge No. 12 (DB 12). The equipment in these buildings was designed to gather and display data from a network of 600 sensors, and provide centralized operator controls for use during Jacket lowerings and pile driving operations.
The primary control building was a two-storied steel building designed for single lift crane moves. The building measured 42' long, 29' wide, 30' high and weighed 175 kips.