Dynamic Positioning (DP) is a computer-controlled system that allows vessels to hold position and heading in a location that is otherwise too deep to launch anchors. DP is achieved by integrating the control units of all thrusters onboard the vessel into a single computerised system. The system, commonly known as the DP system, uses a carefully constructed algorithm to provide a continuous and responsive thrust vectoring on all three degrees of freedom of the vessel (yaw, surge, and sway) to keep the vessel in the same position and at the same heading. Without the DP system, offshore activities such as personnel transfer, subsea pipe-laying, and offshore construction will be risky if not impossible.
DP started to be applied to offshore oil industry assets on a large scale in the early 1980s, particularly with the exploration of the North Sea and deeper water oil and gas fields worldwide. With drilling moving into ever deeper waters, Jack-up barges could not be used any more, and anchoring in deep water was not economical. The initial DP system development had begun in the USA with drilling ships in the late 1960s and early 1970s.
The DP system is made up of 4 main sensors – Gyrocompass, Anemometer, Vertical Reference System (VRS) and Position Reference System (PRS). The gyro measures the heading of the vessel; the anemometer measures the wind speed and wind direction; the VRS measures the pitch, roll and heave of the vessel and the PRS determines the position of the vessel. There are 2 types of PRS – Relative PRS and Absolute PRS. The Relative PRS consist of CyScan, SpotTrack, Fanbeam, RadaScan, RADius, Light Tautwire and HiPAP, while the Absolute PRS consist of DGNSS.
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