A risk-based approach to developing design temperatures for vessels operating in low temperature environments

Increasing activities in the Arctic and Antarctic waters have drawn awareness of the risks of shipping in these regions. Winterization of vessels needs to be considered at the design stage to mitigate the risk of icing, freezing or other damages due to low temperature. The temperature that should be used for design and equipment procurement specification must be defined. Classification societies have proposed design temperatures such as the design service temperature (DST) and the minimum anticipated temperature (MAT). The DST is selected to be at the lowest mean daily average for the operational window and geographical location. However, there is very limited guidance provided to define the MAT. The lack of analytical tools that can be used to develop design temperatures still remains a problem. This paper proposes a risk-based approach to estimate minimum anticipated temperature as design temperatures for vessels intended for service in cold regions such as the Arctic and Antarctic. Hourly air temperature data from climatology stations in these regions were obtained from the website of the National Climatic Data Center (NCDC) which is affiliated to the National Oceanic and Atmospheric Administration (NOAA). The criteria used to select the stations include the time span of available data for at least 20 years, availability of hourly data, and altitude of the station (close to sea level). The analysis procedure involves statistical analysis, consequence quantifications and risk calculations. Results from a case study show that the proposed methodology can be reasonably applied. As the minimum anticipated temperature was obtained by looking at the smallest risk with corresponding larger return period or the smallest probability of occurrence. It is expected to have the smallest risk when the minimum anticipated is applied. In addition, an extreme low temperature contour map of the Arctic region has been developed which provides a quick and useful way to evaluate the temperature profile for voyage planning and winterization requirements. A plot of the ship's route on the extreme low temperature contour map will provide information on the magnitude and duration of the extreme temperatures encountered by the ship during the journey.