Spray Icing on ONEGA Vessel- A Comparison of Liquid Water Content Expressions

Abstract

The hazards associated with ice accretion primarily due to impinging freezing sea spray on ship structures are considered among serious safety concerns for ships operating in the colder regions. An accurate sea-spray icing-estimation model to evaluate the ice accumulation during operations in these regions can make marine operations safer. The accuracy of the present icing models for estimating icing on ships is substantially dependent on the incoming spray flux generated by the wave-ship interaction. In order to illustrate this, the vessel icing incident of the fishing vessel ONEGA is considered, which capsized after encountering heavy icing. In this study, the ONEGA vessel is modeled using a stability-calculation program. Then assuming the vessel to maintain minimum stability criteria prior to icing, the minimum likely amount of ice accumulation in the exposed locations that destabilized the vessel is estimated. This estimation is compared against another method used to evaluate ice thickness over the period ONEGA was accreting ice. The latter method utilizes the operational weather forecasting model used by MET Norway — “Marine-Icing model for the Norwegian COast Guard (MINCOG)”. The MINCOG model uses spray-flux estimations based on past empirical observations mainly obtained from fishing trawlers. The spray-flux consists of important elements like the liquid-water content (lwc) and the spray-generation frequency. An analysis is carried out applying different formulations for these two elements proposed by different researchers to see the variation in evaluating the total ice accumulation. After noticing the difference in results in total ice thickness from the stability and the icing-model methods used in this study, it is concluded that more investigation and field measurements are needed concerning the neglecting of the contribution of wind-generated spray in the spray flux formula used in MINCOG. Accordingly, multiple real-time spray measurements to develop a more suitable spray-flux formulation may improve the ice accumulation estimation over a longer time period.