DP offshore operations require that the vessel reference point is controlled in relation to a fixed reference frame. In some cases, the heading is allowed to change, searching for an adequate angle in which the environmental conditions induce small loads in the hull and minimum DP power is required to keep the position. This DP mode is usually referred as “weathervane control”.
There is no exact method to determinate the minimum energy heading of a vessel in real-time with only the sensors available in a DP system. Therefore, some control strategies were developed in order to control the vessel heading, and estimate the optimal value.
This paper addresses the analysis of the final equilibrium heading of several published weathervane control strategies for two different DP vessels: a typical DP tanker and an asymmetrical DP crane-barge. A static procedure is used to calculate the final heading and the DP power and thrust demand for each controller.
Several environmental combinations of wind, current, local sea-waves and swell are considered, with a systematic variation of the intensities and the direction of the environmental agents.
For non-aligned environmental agents, differences in the final heading are verified for the zero yaw and zero sway strategies. These headings are also compared to the exact minimum power heading, obtained by an optimization procedure considering the DP thrust allocation.