Dynamic positioning

Dynamic positioning (DP) is a computer-controlled system to automatically maintain a vessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors, and gyrocompasses, provide the computer with information about the vessel's position and the magnitude and direction of the environmental forces affecting it. Examples of vessel types that employ DP include ships and semi-submersible mobile offshore drilling units (MODU), oceanographic research vessels, cable layer ships, and cruise ships. The computer program contains a mathematical model of the vessel, including information such as its current drag and thrusters' locations. This knowledge, combined with sensor data (e.g. wind), allows the computer to calculate the required steering angle and the output for each thruster to support operations at sea where mooring or anchoring is not feasible due to deep water, seabed congestion (pipelines, templates), or other constraints. Dynamic positioning may be either absolute, in that the position is locked to a fixed point on the bottom, or relative to a moving object, such as another ship or an underwater vehicle. One may also position the ship at a favourable angle to the wind, waves, and current, a practice called Weathervaning. Dynamic positioning is used by much of the offshore oil industry, for example, in the North Sea, Persian Gulf, Gulf of Mexico, West Africa, and off the coast of Brazil.