Editing Dynamic positioning (section)

{{short description| Automatic ship station- and heading-holding systems }}
{{More footnotes|date=June 2010}}
[[Image:Toisa Perseus&Discoverer Enterprise.jpg|thumb|300px|Offshore support vessel ''Toisa Perseus'' with, in the background, the fifth-generation deepwater [[drillship]] ''[[Discoverer Enterprise]]'', over the [[Thunder Horse Oil Field]]. Both are equipped with DP systems.]]

'''Dynamic positioning''' ('''DP''') is a computer-controlled system to automatically maintain a [[marine vessel|vessel]]'s position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and [[gyrocompass]]es, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. Examples of vessel types that employ DP include ships and [[semi-submersible]] mobile [[offshore drilling]] units (MODU), oceanographic research vessels, [[Cable layer|cable layer ships]] and [[cruise ship]]s.

The computer program contains a [[mathematical model]] of the vessel that includes information pertaining to the wind and current drag of the vessel and the location of the thrusters. This knowledge, combined with the sensor information, allows the computer to calculate the required steering angle and thruster output for each thruster. This allows operations at sea where mooring or anchoring is not feasible due to deep water, congestion on the sea bottom (pipelines, templates) or other problems.

Dynamic positioning may either be absolute in that the position is locked to a fixed point over the bottom, or relative to a moving object like another ship or an underwater vehicle. One may also position the ship at a favorable angle towards wind, waves and current, 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]]. There are currently more than 1800 DP ships.<ref name="Nautinst" />