A General Approach for Dynamic Positioning Weathervane Control

AbstractEnergy efficient controllers for dynamic positioning (DP) systems are a possible approach to reduce energy consumption and CO2 emission on large offshore systems. Due to the flexibility of some DP operations, it is possible to change the vessel heading in order to align with the resultant force defined by the environmental conditions, reducing the thrust and power required to keep position, thus increasing station-keeping capability. However, online calculation of the optimum heading may not be possible because of uncertainties about wave and current intensity and direction. Moreover, these factors change through time, and the system must be able to adapt to those changes and to keep the optimum positioning. This paper presents a new methodology to define the heading setpoint based on zero power control theory. This methodology has important advantages over traditional weathervane control methods, such as an effective control of all horizontal degrees of freedom of the vessel and the possibility to define any reference control point, not only points located at the vessel bow.