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Marine & Station Keeping
DP Position Reference Systems
DP Position Reference Systems measure where the rig is and feed that position to the DP controller. The Category covers DGNSS receivers and antennas, hydroacoustic systems with hull transceivers and seabed transponders, taut wire systems, and laser and radar references. It includes the hull units, gate valves, poles and spare transponders that come with them.
How the controller uses references
The controller weights each reference by its measured quality and rejects any that jump, freeze or drift away from the others. With two references it cannot tell which one is wrong, so Class 2 and Class 3 need at least three references available at the same time. Good practice is to use different principles, because several DGNSS receivers on one correction service can fail together. On a deepwater drillship the usual set is two DGNSS systems and one or two hydroacoustic systems.
Configurations
| Type | Principle | Limits |
|---|---|---|
| DGNSS | Satellite position with differential or precise point corrections | Ionospheric activity, shading, correction link |
| Hydroacoustic USBL | Range and bearing from a hull transceiver to a transponder | Noise, ray bending, water depth |
| Hydroacoustic LBL | Ranges to an array of seabed transponders | Array deployment and calibration time |
| Taut wire | Angle of a tensioned wire to a seabed weight | Practical only in shallower water |
| Laser and radar | Range and bearing to a target on a nearby structure | Line of sight to the target |
Kongsberg HiPAP and Sonardyne Ranger 2 are common acoustic systems on drilling units. Veripos and Fugro supply DGNSS correction services. Fanbeam, CyScan and RadaScan are the usual laser and radar references near platforms.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Constellations and frequencies | Availability and accuracy | GPS, GLONASS, Galileo, BeiDou, L1/L2/L5 |
| Correction service support | Needed for DP accuracy | Provider and service level |
| Acoustic mode | USBL, LBL or combined | Mode list from OEM |
| Depth rating | Transponder and system range | m (ft) |
| Hull unit | Transducer deployment | Hoisted pole, gate valve size |
| Output | Controller compatibility | Telegram format, serial or network |
Standards and guidance
- IMO MSC/Circ.645 and MSC.1/Circ.1580 set the reference count for each equipment class, and Class 3 requires one reference connected to the back-up DP system.
- Class rules for DP notations require type-approved or accepted references and witness their function in trials.
- IMCA M 103 and the MTS DP operations guidance cover reference selection, independence and how references fail.
- Annual DP trials to IMCA M 190 test reference failures and rejection.
Failure modes and inspection
- Acoustic hull units suffer worn hoist gear, leaking gate valves and damaged transducer faces. Inspect the pole, seals and hoist, and run the hoist through its full stroke.
- Transponders need battery changes and servicing of seals, release mechanisms and flotation. Check the battery date and depth rating.
- Transducer performance drops with damage or age. Ask for a recent calibration and a harbour or field test.
- DGNSS antennas and cables degrade with weather exposure. Check the cable runs and the antenna mounts for corrosion.
- Taut wire systems wear their wire, sheaves and tension cylinders. Check the wire and the gimbal head.
Documentation
- Type approval and class acceptance for DP use.
- Calibration records, including the acoustic system's alignment to the vessel frame.
- Transponder service records with battery dates.
- Firmware and software versions.
- The last DP trials report showing the reference in service.
Integration
Check that your DP controller supports the reference model and its output message. An acoustic hull unit needs a matching gate valve and hull penetration, and its transducer must be aligned to the vessel's reference frame with gyro and motion sensor offsets. A DGNSS receiver needs a correction subscription in your name, because the subscription does not move with the hardware. The receivers themselves overlap with GPS and GNSS Receivers.
Service and the used, surplus or refurbished choice
Transponders and DGNSS receivers often come as spares from retired rigs, and an OEM service with new batteries and seals makes them fit to deploy. A used hull unit sits below the waterline, so treat it as a refurbishment job with new seals and a hoist inspection. Unused surplus acoustic systems from cancelled newbuilds can match sister drillships. The controller that consumes these signals is in DP Control Systems.
FAQ
Frequently asked questions
How many position reference systems does a DP2 rig need?
A DP Class 2 or Class 3 rig needs at least three position references available at the same time. With only two, the controller cannot tell which one is wrong when they disagree. Guidance also asks that they use different principles, such as satellite and acoustic.
Do used seabed transponders need servicing before deployment?
Yes, used transponders need new batteries and a service of seals, release mechanisms and flotation before they go back to the seabed. Ask for the battery date, depth rating and last service record. An OEM or approved workshop should test them before use.
Does a DGNSS correction subscription transfer with a used receiver?
No, a correction service is a contract between the provider and the user. You set up a new subscription for the receiver, so first check the provider still supports that model in your area. Some older receivers cannot decode current correction formats.
Is a taut wire still useful on a deepwater drillship?
Rarely, because a taut wire works only in shallower water where the wire angle stays measurable. Deepwater drillships rely on DGNSS and hydroacoustic references instead. Taut wire remains useful on semis and other units working in moderate water depths, where it gives a reference independent of satellites and acoustics.
What should I check on a used acoustic hull unit?
Check the gate valve, the hoist and the transducer face first, since all three sit at or below the waterline. Run the hoist through its full stroke, inspect the seals and ask for calibration records. Plan an OEM alignment after installation.
Looking for DP position reference systems?
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