Estimating the likelihood of weather criteria exceedance during marine operations

This paper describes an approach to estimating the probability of marine operations being exposed to unsafe weather conditions. Marine operations, both inshore and offshore, are normally sensitive to environmental conditions. For the majority of operations threshold weather criteria will be predefined. An estimate of the likelihood of the operation experiencing 'bad' weather, taking into account the uncertainties in weather forecasting, is of great value. The method is intended to be used as part of a risk assessment of marine operations, enabling the impact of design and scheduling decisions to be assessed in a structured and systematic way. The method has two components. Firstly, the time to complete an operation is defined in the form of a probability/time distribution. This is done by analysing the duration of the tasks within the operation and identifying possible causes of delays. The likelihood and duration of each delay is estimated. Secondly, a probability/time curve is defined for the weather conditions exceeding the predefined threshold. The curve is determined by reference to the location of the marine operation, the time of year of the operation, the initial weather conditions and the accuracy of weather forecasting. Using the two probability/time curves, the likelihood of exposure is calculated.