Wales, S., Swaik, G., Yik Ting, K., Jayasinghe, K., Gumley, J. and Potts, A.E. (2016). Published in APPEA Journal 2016.

There has always been a clear need to demonstrate that project critical offshore heavy lifts can be conducted safely, within allowable criteria, for the metocean conditions likely to occur in-field. Extensive guidance is available in the design codes for lifts subsea but, for lifts in air, dynamic analysis of the response of a suspended mass is not fully addressed. Analyses generally yield results that do not agree well with operating experience and cannot easily be assessed against the limited code guidance available. Traditionally, operator skill and experience has thus been relied on to justify the operability of such lifts. Recent experience in engineering the lift of a 500 te module onto the Yolla platform in Bass Strait, Victoria, has further underlined the deficiencies in analytical techniques and approaches available to the industry.

This paper presents experience gained from the pre- and post-lift analysis of an instrumented lift operation recently conducted by the mono-hull vessel Sapura 3000 in the challenging environmental conditions of Bass Strait. This analysis was used to demonstrate that the lift could be conducted safely within tight operational constraints, meeting the codified criteria set.

Subsequent analysis of data gathered during the lift was used to explore and refine modelling assumptions to aid the engineering of future challenging heavy lifts. The analyses conducted advanced the state‑of‑the‑art work in this field for the offshore industry.
By enabling numerical techniques for heavy lifts, which are typical of many other offshore operations, safety will be improved, project contingencies can be properly estimated through more accurate prediction of downtime, and cost savings can be achieved by the selection of more effective vessels for the task.