Reliability Analysis of Gyrocompass Systems in Offshore Supply Vessels Under Hydro-Meteorological Disturbances and Its Implications for Oil Spill Risk

This study presents a methodology for assessing thereliability of navigation systems in offshore operations, accounting for hydro-meteorological variability and its implications for environmental risk. A semi-Markov model is developed to characterise transitions between hydro-meteorological states. The approach is applied to a gyrocompass system installed aboard an offshore supply vessel operating in the North Sea under varying wind and wave conditions. The system consists of three redundant gyrocompasses, with alarms triggered by deviations exceeding 2° from the median value. Data collected over an 18-month period are used to estimate the durations of individual hydro-meteorological states and the associated state-transition characteristics, which are subsequently incorporated into the reliability analysis. The resulting alarm-related reliability estimates are then integrated into a probabilistic framework linking deviations in gyrocompass readingsto potential loss of navigation performance, accident occurrence and oil spill risk. These estimates are based on operational heading-deviation alarm data, while the conditional risk probabilities are calculated using literature-informed parameters and values adopted for the illustrative risk scenario.Under the assumption of independent gyrocompass events, the three-gyrocompass configuration improvesthe modelled system reliabilityand yields arelative reduction of approximately 76.66% in the estimated oil spill probability for the considered time horizon, compared with a single-gyrocompass configuration. This reduction is specific to the adopted risk scenario. The framework therefore provides a basis for risk-informed decision-making in offshore vessel operations.