**2.1 DP elements**

Any DP system always has seven segments or elements, namely: controller, DP console, Dynamic Positioning Operator (DPO), position reference systems (PRS), motion reference units (MRU), propulsion and power supply. Each element will be described in this section.

The central element is the controller, composed of computers or processors, which sets a two-way communication with all other DP elements via the vessel network.

The system is controlled with the help of the DP console, which contains operational controls, buttons, screens and a manual joystick.

The DP console is controlled by a Dynamic Positioning Operator (DPO) who should be fully certified to conduct DP operations.

To acquire information on the position of the rig, PRS are used. In DP drilling operations, several PRS provide additional accuracy [1]. Usually, a drilling rig will select dual differential global navigation satellite system (DGNSS) and hydro-acoustic positioning references (HPR), usually of the long-baseline type. Taut wires are only used in shallow waters, as they are not available in deep water [2].

The motions of the vessel are monitored with different sensors. The yawing is monitored with the help of one or more gyrocompasses which send information about the heading. Different MRU help send information about surge and sway.

The wind and current are also monitored for course and speed, and this information is sent to the controller. There are different wind sensors in different positions onboard the rig to avoid errors due to windscreens, turbulences provoked by structures, and other obstacles.

With all this information, the controller can predict the movement on the vessel and send a proper command to the propellers and thrusters (pitch, revolutions per minute, azimuth, rudder angle) to counter-rest the forces and maintain the rig in the desired position.

A vital part of the DP system is the power supply. Diesel, alternators, switchboards, cabling, propulsion motors and power-management form part of the power system related to the DP operations [3].
