On the Likelihood of Encountering Design Conditions During Heavy Transport - A Case Study of 56 Replicate Voyages From Korea to the Suez Canal

A critical element in heavy transport design is the identification of design wave conditions. Since most transports are one-of-a-kind, statistically meaningful comparisons of observed vs. design conditions are nonexistent. The present paper examines the experience from a recent oil and gas giga-project, encompassing 56 replicate voyages from Korea to the Suez Canal. In doing so, this paper provides an anchor point for assessing the real-world likelihood of exceeding design wave conditions during heavy transport. Voyage maximum wave conditions from the 56 replicate voyages are found to closely follow a Weibull distribution, allowing for the ready evaluation of observed 1-in-N voyage extremes. These observed wave conditions are compared with corresponding design values on both a year-round and seasonal (3-month) basis. Three important observations are drawn from these comparisons. First, operating limits established by heavy transport contractors to avoid waves above a predetermined threshold do not eliminate the need to design for higher wave conditions. Over the 56 replicate voyages studied, observed wave conditions slightly exceeded the contractor's self-imposed operating limit (i.e., by approximately 10% or less) on five separate voyages; on a sixth voyage, this same operating limit was exceeded by approximately 40%. Second, simplified tools for evaluating design wave conditions using Global Wave Statistics do not consistently estimate the 1-in-10 voyage extreme. While the simplified approach is shown to be conservative for the route studied, the associated design margin varies considerably throughout the year. Third, SafeTrans voyage simulations are observed to well-predict the 1-in-10 voyage extreme for the route studied.