Bullwinkle Loadout Analysis

ABSTRACT The Bullwinkle jacket was loaded onto a launch barge using a conventional skidding operation. The size (over 1365 feet long), weight (approximately 50,000 tons), and stiffness characteristics of this jacket made it necessary to control relative deflections during loadout to a high degree of accuracy. Computer analyses were performed to determine the requirements of the fabrication yard and launch barge support structures which would assure no overstressing of jacket components during the loadout operations. A computer assisted survey/data gathering system was used to compare the jacket/barge deflections during loadout to the predicted and allowable values. A summary of the analyses, the survey/data gathering system, and their combined function is given in this paper. A comparison of the actual jacket barge behavior to the predicted and allowable behavior is discussed. It is concluded that through the use of information and confidence gained from the analyses and on-site survey/data comparison system described in this paper, many cost saving operation/construction techniques were implemented on items associated with the jacket and the fabrication-yard skidway. GENERAL Construction of the Bullwinkle jacket began in June, 1985 and it was loaded onto a barge for transport to the offshore installation site in May, 1988. An overview of this project is presented in more detail in reference 1. The jacket was assembled lying on its side, with its top end located nearest the waterfront bulkhead. Dulling fabrication there were yard supports beneath all four of the major longitudinal truss rows for the entire length of the jacket. Just prior to loadout all temporary supports were removed, leaving the jacket supported only by the skidway beneath truss rows A2 and A3. Figure 1 depicts the jacket on the fab-yard skidway prior to loadout. A more complete description of the fabrication procedures are given in Reference 2. The barge used to transport the jacket to the offshore installation site had plan dimensions of 207 feet wide by 853 feet long, giving it a deck load carrying capacity of approximately 10,800 kips per foot of draft at the depth selected for the Bullwinkle jacket loadout. The dimension between the A2/A3 skidways was 140 feet and the tilt beam length was 200 feet. During the loadout operation the barge was moored with its bow toward the fab-yard bulkhead with a clear span between the skidways of the yard and the barge of77 feet. Mer loadout the jacket was positioned on the barge with the top 350 feet of the jacket extended past the end of the tilt beam and the bottom end cantilevered off the bow of the barge approximately 68 feet.(Figure 2) Because of the relative dimensions of the jacket and barge, along with the center-of-gravity of the jacket being located approximately one-third of the jacket length from its trailing end, the weight transfer from the fab-yard to the barge was predicted to be very non-uniform.