Analytical Predictions and Field Observations of the Loadout Operations of the' Kilauea Jacket
Authors: Sircar S. , Chandra T.K. , Mills T.R.J. , Roberson W.P. , Schultz A.R. 
Published: October 2008

The Kilauea jacket was loaded out on the launch barge Intermac 650 by conventional skidding. The 8,100 ton, 645 feet long, relatively rigid stiffness characteristics of the jacket, required that the deflection of the barge and the jacket during load out be controlled accurately. Crane assist during load out was used to reduce the jacket's stresses and joint can thicknesses.

A stepped ballasting procedure wasdeveloped which resulted in an 'almost level load out'. This ensured that jacket deflections remain within allowable deflection envelopes. A computer assisted survey system was used during load out to compare measured barge/jacket deflections to predictions. The load out analysis and results, a description of the survey system, a narrative of the actual load out operation and a comparison of the observed barge/jacket behavior with the predicted behavior are presented. This proven load out procedure resulted in the Kilauea jacket being loaded out in less than seven hours while keeping the jacket deflections within allowable envelopes. Comparison of predicted barge deflections and site survey measurements showed acceptable differences.

LOADOUT OVERVIEW

Detail engineering of the Kilauea jacket began in December 1987 and fabrication in May 1989. The jacket was loaded out on to the launch barge Intermac 650 (1-650) in June 1989 from McDermott's Morgan City fabrication yard. Details of the design process and fabrication are discussed in references 1 and 2. The jacket was fabricated on its side with the base of the jacket 60' from the waterfront. During load out, the stern of the free floating I-650 faced the bulkhead. This is schematically shown in Figure 1. At load out, the water level in the bayou required the barge draft to be 30.5' to align the top of the barge launch ways with the fabrication yard skid ways. Pull bars were used between the I-650 hydraulic jacks and the jacket's loadout-launch lugs.

Extensive analysis demonstrated that the barge could be deballasted fast enough to complete the load out in less than seven hours keeping the barge launch ways aligned with the fabrication yard skid ways. Analysis also demonstrated that at all stages of ballast changes, the selected ballast distributions would keep the barge deck deflection within acceptable limits.

BARGE DEFLECTION CONTROL PHILOSOPHY

To develop the allowable jacket deflection envelopes, the load out analysis assumed a rigid barge with a flat deck. The use of this assumption is justified if it is demonstrated that during all stages of load out, the barge deck can be kept flat. There are two aspects that help to make the rigid barge assumption acceptable; (1) the Kilauea jacket is light compared to the barge displacement and (2) in the final position after load out, the overhang at the stern of the barge is small with no overhang at the bow. This means that the jacket's structural stiffness would not significantly influence the midship section modulus and hence the longitudinal deflected shape of the barge. As a result conventional, ship strength based deflection calculation methodology, can be used to predict the longitudinal deflection of the barge for a given loading condition.