DP and Class 3 rules
Dynamic Positioning (DP) is a computer-controlled system to automatically maintain a vessel’s position and heading by using its own propellers and thrusters. Acoustic position reference sensors, combined with wind sensors, motion sensors and gyrocompasses, provide information to the computer pertaining to the vessel’s position and the magnitude and direction of environmental forces affecting its position.
The International Maritime Organisation (IMO) categorises vessels into different classes depending on the and duties it will be carrying out. The most stringent of these is Class 3 and states that, amongst other requirements, loss of position should not occur from any single failure including a completely burnt fire sub division or flooded watertight compartment. Examples of DP Class 3 vessels operating with the offshore and energy sector include FPSOs, mobile drilling units, construction vessels and well intervention vessels.
Economic climate and vessel utilisation are now obvious drivers to increase the efficiency of vessel operations. Choosing the right acoustic position reference (sometimes known as HPR) for your DP 3 vessel will deliver efficiency savings for both you and contracting oil company by reducing the number of seabed transponders, reducing overall system maintenance requirements and employing the vessel’s acoustic reference system to perform survey, construction and monitoring tasks as well as DP.
It is important that efficiency savings are delivered without compromising the integrity of the DP reference. Our Wideband digital technology delivers the highest possible accuracy and reliability but easy to use software is equally important so that DP operators can make full use of its potential.
Inertial navigation complements Wideband digital acoustic signals, with high integrity inertial measurements. It is important to choose an inertial navigation solution that is tightly coupled with the acoustics, with the INS co-located with the acoustic transceiver if the performance and efficiency gains are to be achieved. A tightly coupled INS solution is resilient to acoustic disruptions meaning between only one and three transponders per system are needed rather than a full array. The high update rate (1Hz) position solution sent to the DP system more closely matches the GNSS data rate and the vessels dynamic model leading to more robust station keeping when compared to conventional configurations.
Operationally, it is important to choose a DP reference that is compatible with subsea survey, construction and ROV operations as well as considering requirements for DP. Compatibility with our subsea equipment that is used in 95% of deepwater projects is an important consideration. Survey, ROV and dual independent acoustic DP references can safely share a seabed array of transponders using “subscription mode” which will allow multiple users to “subscribe” to transponder channels. This offers flexibility to allow a dual independent system to share an array or for an ROV to operate in parallel using the same seabed transponders without risk of interfering with the DP.