The leeway of shipping containers at different immersion levels

Abstract

The leeway of 20-ft containers in typical distress conditions is established through field experiments in a Norwegian fjord and in open-ocean conditions off the coast of France with a wind speed ranging from calm to 14 ms −1 . The experimental setup is described in detail, and certain recommendations were given for experiments on objects of this size. The results are compared with the leeway of a scaled-down container before the full set of measured leeway characteristics are compared with a semianalytical model of immersed containers. Our results are broadly consistent with the semianalytical model, but the model is found to be sensitive to choice of drag coefficient and makes no estimate of the crosswind leeway of containers. We extend the results from the semianalytical immersion model by extrapolating the observed leeway divergence and estimates of the experimental uncertainty to various realistic immersion levels. The sensitivity of these leeway estimates at different immersion levels are tested using a stochastic trajectory model. Search areas are found to be sensitive to the exact immersion levels, the choice of drag coefficient, and somewhat less sensitive to the inclusion of leeway divergence. We further compare the search areas, thus, found with a range of trajectories estimated using the semianalytical model with only perturbations to the immersion level. We find that the search areas calculated without estimates of crosswind leeway and its uncertainty will grossly underestimate the rate of expansion of the search areas. We recommend that stochastic trajectory models of container drift should account for these uncertainties by generating search areas for different immersion levels and with the uncertainties in crosswind and downwind leeway reported from our field experiments.

A Stokes drift approximation based on the Phillips spectrum

“…Here the averaging is over a period appropriate for the frequency of surface waves (Leibovich, 1983). The Stokes drift velocity profile is required for a number of important applications in ocean modelling, such as the computation of trajectories of drifting objects, oil and other substances (see McWilliams and Sullivan 2000, Breivik et al 2012, Röhrs et al 2012, Röhrs et al 2015and references in Breivik et al 2013. Its magnitude and direction is required for the computation of the Stokes-Coriolis force which enters the momentum equation in Eulerian ocean models (Hasselmann 1970, Weber 1983, Jenkins 1987, McWilliams and Restrepo 1999, Janssen et al 2004, Polton et al 2005, Janssen 2012,…”

OpenDrift v1.0: a generic framework for trajectory modelling

“…Nonlinear processes, such as evaporation of oil or capsizing of vessels, are disabled in backtracking mode. This simple backtracking scheme is an easy-to-use alternative to more complicated inverse methods, such as iterative forward trajectory modelling (Breivik et al, 2012b), and is also much less computationally expensive.…”

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When Tragedy Strikes: Potential Contributions From Ocean Observation to Search and Rescue Operations After Drowning Accidents

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