Captain Alex Simpson explains how Dynamic Positioning helps with ocean drilling
The JR’s Dynamic Positioning System (DP), supported by 12 powerful thrusters and 2 propellers, uses computers to maintain the ship over a specific location while drilling in waters as deep as 8,200 meters (5 miles, 27,000 feet). The desired position for ocean drilling activities is entered into the DP computers, then data from two global positioning systems, better know as GPS, and one hydro acoustic beacon on the seabed are fed into the DP computers to give a real time position. If the ship moves from the desired position, these data are processed and a resultant force is applied by the thrusters and propellers to move the ship back to the desired drilling location. A gyro compass input ensures the ship's heading is maintained in the same way.
While GPS is relatively new technology, what about the old technology of a seabed beacon producing a sound signal or "ping" on the seabed? A signal is produced every second and speeds its way through the water, which, incidentally, is about 4.4 times faster than the speed of sound in air or 4,940 km per hour (3,355 miles per hour). The sound signal is received by five hydrophones deployed beneath the vessel's hull. A precise measurement of the time difference between each pair of hydrophones hearing the "ping" allows the computer to process the data. This calculates the position of the ship relative to the beacon using a simple hyperbolic navigation system discovered decades ago. Some say it was used in the First World War with hand calculations, and was certainly used during the Second World War by means of radio waves and radio receivers. However, modern technology means faster and more accurate calculations.
For more information about dynamic positioning, watch our video on the scientific drilling process.
Photo: Panoramic view of the Dynamic Positioning System on The JR's bridge. Credit: Bill Crawford, IODP Imaging Specialist.