A Methodology to Analyze, Treat and Guarantee Attendance to Legal Requirements of Light Ship Modifications on Floating Production Units

The constant modifications that are done aboard floating units have direct impact on the safety requirements regarding stability. With few exceptions these modifications imply on onboard construction (e. g. process plant upgrade), and the correspondent rise of light ship weight. The consequence will be negative effect on stability, a reduction of the capacity for future modifications that will probably be necessary as well as the ability to deballast to lower drafts. According the Rules applicable [1], the modification of the light ship weight that surpasses a defined limit must be checked through an Inclining Test that can only be executed with the unit in sheltered waters. For a Floating Production Unit (FPU) this test is unfeasible because of the operational procedure (the need to disconnect anchor lines and risers, tow and reconnect) and the production downtime. The alternative is to negotiate with the Regulatory Bodies a penalty for the light ship modifications that imply in a further reduction on the range of stability and the correspondent capacity of the unit to undergo further and necessary modifications. The motivation of this work is to develop and test a methodology where the light ship modifications that were done through the years undergo audit and the data generated is statistically treated considering the conditions and objectives of the Classification Society’s stability criteria. The result is an acceptable alternative to the inclining test that is consistent with the stability rules that apply, that permits a reduction on the penalties and consequently permits further and most necessary modifications aboard. This methodology has been applied to a semi submersible floating production unit (FPU) operating and going through light ship modifications for 15 years, with very good results. The whole procedure was approved by the Classification Society of the unit.Copyright © 2007 by ASME