Inertial Sensors for Risk-Based Redundancy in Dynamic Positioning

In this paper we present an alternative configuration of sensors, position and heading reference systems for dynamically positioned (DP) vessels. The approach uses a sensor structure based on low-cost inertial measurements units (IMUs), satisfying fault tolerance against single-point failures that is at the essence of the IMO guidelines for both DP class 2 and 3 vessels. Recent results have shown that dual-redundant position and heading reference systems are sufficient to prevent loss of position within some well-defined time horizons by exploiting sensor fusion of the reference systems and triple-redundant MEMS-based IMUs. These IMUs also function as Vertical Reference Units (VRUs), since vessel motions is obtained using the same IMU configuration and sensor fusion framework. In this proposition, the acceleration measurements provided by the IMUs make wind and other force sensors unnecessary, except possibly for an advisory role. The proposed framework has the potential to significantly reduce the cost of dynamic positioning systems without compromising safety.