Control Systems for Upending the Bullwinkle Jacket
Authors: Piter E.S. , Brasted L.K. , Kenney J.J. 
Published: October 2008

The Bullwinkle jacket was upended without the aid of a derrick barge hook load or auxiliary buoyancy tanks. The systems used to control and monitor added ballast water were designed to assure the operation could proceed safely even if inadvertent flooding of jacket chambers occurred. Considerations that led to the decision to upend the jacket through controlled ballasting rather than allowing the jacket to self-upend to near vertical are discussed. Behavior of the jacket during the initial flotation, upending, and set down is summarized. Simplicity of operation, which reduced the potential for operator error, was maintained without sacrificing reliability or redundancy. This was accomplished by designing systems which controlled these operations hand-in-hand with ongoing installation engineering and by a conscientious effort of all involved to develop and implement a comprehensive fabrication yard pressure/functional test program.

INTRODUCTION

The Bullwinkle jacket was installed at its offshore site during the summer of 1988. An overview of the entire project is presented in Reference 1.

A system was incorporated into the Bullwinkle jacket to control the following functions during the initial installation phase:Addition of ballast water to jacket leg chambers.Deballasting of leg chambers, if required.Monitoring of the amount of ballast water in each chamber.Opening of the drain hatches on the four skirted mudmats allowing the escape of entrapped water during the setting of the jacket onto the seafloor, then close the hatches 11;0 assure a watertight seal between the mudmat top plate and soil. Reference 2 gives a more complete description of the design and operational intent of these mudmat drain hatches.

As initially bid, the Bullwinkle jacket had four large diameter auxiliary buoyancy tanks attached to its upper framing, two on each of the outboard vertical rows. These tanks provided adequate reserve buoyancy such that even if significant inadvertent flooding of several of the jacket legs occurred after launch, the jacket would remain afloat in a stable condition. With this configuration, an upending procedure was developed that would allow the lower part of two legs to fill with ballast water prior to any operator action. The jacket would rotate to a near vertical position after this flooding had taken place. At that time personnel could board the jacket and perform operations allowing ballast water to enter other selected leg chambers, causing the jacket to sink to the seafloor.

Through careful selection of framing members during the final jacket design, a configuration was developed which had approximately 8 to 10% reserve buoyancy without the use of auxiliary tanks; therefore, installation methods which would eliminate auxiliary buoyancy tanks were reviewed. Reference 3 describes this design process more fully. Table No.1 summarizes the final jacket weight and buoyancy characteristics. A contingency of 2 1/2% was added to the calculated "nominal" jacket weight during all upend and set down computer analyses. This accounted for steel mill tolerance, weld metal, paint, and other small miscellaneous appurtenances not included in the calculated material take-off.