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Development of a Inclining Test Procedure Applicable to Semi Floating Production Units Moored on Location

[+] Author Affiliations
Sérgio Nogueira

Petrobas, Rio de Janeiro, Brazil

Paper No. OMAE2009-79184, pp. 163-168; 6 pages
  • ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 1: Offshore Technology
  • Honolulu, Hawaii, USA, May 31–June 5, 2009
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4341-3 | eISBN: 978-0-7918-3844-0
  • Copyright © 2009 by ASME


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 a negative effect on stability, and because the semi submersible has a very low stability margin, 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 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 the undergo further and necessary modifications. The motivation of this work is to develop an Inclining Test procedure that can be applied to semi submersible floating production units moored on location, without the need to tow to sheltered waters, which will yield results as accurate as the ones obtained through the conventional Inclining Test, and also accepted by the main Classification Societies. To achieve this it is necessary to first determine the accuracy of the conventional Inclining Test accepted by the Classifications Societies by means of a detailed statistical analysis. Then innovations are proposed in the instruments used to measure de physical parameters, the hydrostatic relation between moment and angle, and the test procedure itself with much better accuracy compared to the conventional procedure. Reliable and tested computational tools are developed to model risers and mooring line forces to determine their effect, and statistical tools are proposed to filter wind and wave influence. The result is an acceptable alternative to the conventional Inclining Test that is consistent with the stability rules that apply, permits a reliable determination of the main stability parameters, reduction on the penalties and consequently further and most necessary modifications aboard. This work is based on the author’s thesis for a Masters Degree at COPPE/UFRJ, currently underway at the Graduate Engineering Project Coordination at Rio de Janeiro Federal University.

Copyright © 2009 by ASME
Topics: Mooring



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