Investigation of two pack ice besetting events on the Umiak I and development of a probabilistic prediction model

Abstract

Pack ice besetting events are defined as incidents in which a typical ice-class vessel encounters dynamic sea ice conditions which are beyond the ship's icebreaking and maneuverability capacities, and the vessel becomes stuck in the pack ice until such conditions subside. Besetting events can cause severe disruption to a vessel's transit schedule, leading to increased operational downtime, and ship crew and fuel costs. Hence, predicting the probability of occurrence of these events can help vessel operators plan in advance accordingly, possibly rerouting the vessel, and saving operational costs. In this paper, two pack ice besetting events experienced by the Umiak I, an icebreaking bulk carrier owned and operated by Fednav Limited which runs nickel ore from the mine at Voisey's Bay, Labrador to Québec City, are analyzed in terms of the wind, surface ocean current, and sea ice conditions which caused them. The particular metocean and pack ice conditions associated with the occurrence of these events are used to develop a framework for a model to predict the future occurrence of such events for the Umiak I and quantify probabilities of besetting event occurrence linked to specific sets of coincident metocean and ice conditions. The model will serve as a tool for predicting besetting event probabilities during Umiak I navigations, as well as in hindcast shipping feasibility studies, to determine the likelihood of besetting for vessels with Umiak I capabilities in regions of new operations. The factors considered in this study are the vessel distance to the nearest coastline, regional wind and surface current speed, direction relative to the nearest coastline, divergence, and vorticity. The ice factors considered are the total concentration, mean thickness, and floe size (this represents a mean floe diameter). The datasets analyzed in this paper suggest the primary causes of the two besetting events experienced by the Umiak I in 2012 and 2013 were the relatively large ice floes encountered by the vessel (the majority of the floes during the besetting events were greater than 6 km in diameter), in combination with a convergent regional wind field and onshore winds and currents.