No one disputes the statement ‘A Dynamic Positioning (DP) system can never become better than its references'.
Automatic control of a vessel's position in a critical operation or location requires good redundancy of all the control system components. Whether it is a vessel's position extremely close to a fixed platform, or a construction platform vessel for a critical deep underwater installation, it will require automated, accurate and controlled position keeping.
A DP system is a controlling computer that feeds the thrusters and propellers with accurate signals of power required to hold the position of the vessel, or to move it in a controlled fashion from one position to another, in any environmental weather condition. The DP cannot function without input from position reference systems and operates often with many such systems in an integrated solution.
Each position reference system contributes by sending its present logged position data to the DP. Each reference system has different characteristics of strengths and weaknesses. They are often classified according to how stable they are in position accuracy, position deviation and position update rate.
There are many position reference systems available in the market, but when a vessel is alone in the open ocean a long way from shore it is only the satellite based Global Positioning System (GPS) and the seabed transponder based Hydroacoustic Position Reference (HPR) that can give reliable reference positions.
Hydroacoustic Aided Inertial Navigation, or HAIN, will allow the weighting of the HPR to the same level as GPS in the DP algorithm. This is probably the best news for DP reference systems in 20 years!
HAIN systems onboard Seadrill's West Navigator and Ocean Rig's Eirik Raude have been running with excellent results while the vessels have been in drilling operation in 850 and 2700 meter water depth respectively.
The HAIN is an ‘add-on' system to the HiPAP or HPR system and uses either the LBL or the SSBL position output as position aiding in an algorithm that also reads an Inertial Measurement Unit (IMU). An IMU is the sensor in Inertial Navigation System (INS).
After years of development and experience from navigation of the autonomous underwater vehicle HUGIN, the ‘HAIN DP Reference' is now developed using the same technology.With more than a year of field tests, system improvements and proven excellent performance, it is expected that this products will fulfil a huge demand for improved subsea reference for DP systems.