View source for Dynamic positioning

{{short description| Automatic ship station- and heading-holding systems }}
{{copyedit|date=November 2025}}
[[Image:Toisa Perseus&Discoverer Enterprise.jpg|thumb|Offshore support vessel ''Toisa Perseus'' with, in the background, the fifth-generation deepwater [[drillship]] ''[[Discoverer Enterprise]]'', over the [[Thunder Horse Oil Field]]. Both are equipped with DP systems.]]

'''Dynamic positioning''' (DP) is a computer-controlled system to automatically maintain a [[marine vessel|vessel]]'s position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors, and [[gyrocompass]]es, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. Examples of vessel types that employ DP include ships and [[semi-submersible]] mobile [[offshore drilling]] units (MODU), oceanographic research vessels, [[Cable layer|cable layer ships]], and [[cruise ship]]s.

The computer program contains a [[mathematical model]] of the vessel that includes information pertaining to the wind and current drag of the vessel and the location of the thrusters. This knowledge, combined with the sensor information, allows the computer to calculate the required steering angle and thruster output for each thruster. This allows operations at sea where mooring or anchoring is not feasible due to deep water, congestion on the sea bottom (pipelines, templates), or other problems.

Dynamic positioning may either be absolute in that the position is locked to a fixed point over the bottom, or relative to a moving object like another ship or an underwater vehicle. One may also position the ship at a favorable angle towards wind, waves, and current, called weathervaning.

Dynamic positioning is used by much of the offshore oil industry, for example, in the [[North Sea]], [[Persian Gulf]], [[Gulf of Mexico]], [[West Africa]], and off the coast of [[Brazil]]. There are currently more than 1800 DP ships.<ref name="Nautinst" />

==History==
Dynamic positioning began in the 1960s for [[offshore drilling]]. With drilling moving into ever deeper waters, [[Jack-up]] barges could not be used anymore, and anchoring in deep water was not economical.

As part of [[Project Mohole]], in 1961, the drillship [[CUSS I|''Cuss 1'']] was fitted with four steerable propellers. The Mohole project was attempting to drill to the [[Mohorovičić discontinuity|Moho]], which required a solution for deep water drilling. It was possible to keep the ship in position above a well off [[La Jolla]], California, at a depth of 948 meters.

After this, off the coast of [[Guadalupe Island|Guadalupe]], Mexico, five holes were drilled, the deepest at {{cvt|183|m|ft}} below the sea floor in {{cvt|3,500|m|ft}} of water, while maintaining a position within a radius of {{convert|180|m|ft}}. The ship's position was determined by radar ranging to buoys and sonar ranging from subsea beacons.

Whereas the ''Cuss 1'' was kept in position manually, later in the same year, [[Shell Oil Company|Shell]] launched the drilling ship ''Eureka'' that had an analogue control system interfaced with a taut wire, making it the first true DP ship.<ref name=Intro />

While the first DP ships had analogue controllers and lacked redundancy, since then, vast improvements have been made. Besides that, DP nowadays is not only used in the oil industry, but also on various other types of ships. In addition, DP is not limited to maintaining a fixed position anymore. One of the possibilities is sailing an exact track, useful for [[Cable layer|cablelay]], pipelay, survey, and other tasks.

==Comparison between position-keeping options==
Other methods of position-keeping are the use of an anchor spread and the use of a jack-up barge. All have their own advantages and disadvantages.
{| class="wikitable" width="100%"
|+ Comparison of position-keeping options <ref name=Intro/>
|-
|
| style=";width:33.3%;background:#efefef;" align="center"|'''Jack-up barge'''
| style="width:33.3%;background:#efefef;" align="center"|'''Anchoring'''
| style="width:33.3%;background:#efefef;" align="center"|'''Dynamic positioning'''
|-
!'''Advantages'''
|
*No complex systems with thrusters, extra generators and controllers.
*No chance of running off position by system failures or blackouts.
*No underwater hazards from thrusters.
|
*No complex systems with thrusters, extra generators and controllers.
*No chance of running off position by system failures or blackouts.
*No underwater hazards from thrusters.
|
*Maneuverability is excellent; it is easy to change position.
*No anchor handling tugs are required.
*Not dependent on water depth.
*Quick set-up.
*Not limited by obstructed seabed.
|-
!'''Disadvantages'''
|
*No maneuverability once positioned.
*Limited to water depths of 175 meters.
|
*Limited maneuverability once anchored.
*Anchor handling tugs are required.
*Less suitable in deep water.
*Time to anchor out varies from several hours to several days.
*Limited by obstructed seabed (pipelines, seabed).
|
*Complex systems with thrusters, extra generators and controllers.
*High initial costs of installation.
*High fuel costs.
*Chance of running off position in case of strong currents or winds, or due to system failures or blackouts.
*Underwater hazards from thrusters for divers and [[Remotely operated underwater vehicle|ROV]]s.
*Higher maintenance of the mechanical systems.
|}

Although all methods have their own advantages, dynamic positioning has made many operations possible that were not feasible before.

The costs are falling due to newer and cheaper technologies, and the advantages are becoming more compelling as offshore work enters ever deeper water and the environment (coral) is given more respect. With container operations, crowded ports can be made more efficient by quicker and more accurate berthing techniques. Cruise ship operations benefit from faster berthing and non-anchored "moorings" off beaches or inaccessible ports.

==Applications==
[[Image:Sbx underway.jpg|thumb|[[Sea-based X-band Radar|SBX]] underway]]
Important applications include:
*Servicing [[aids to navigation]] ([[ATON]])
*[[cable layer|Cable-laying]]
*[[Crane vessel]]s
*[[Cruise ship]]s
*[[Deep sea mining]]
*[[Diving support vessel]]s
*[[Dredging]]
*[[Drillship]]s
*[[Floating production storage and offloading]] units (FPSOs)
*[[Flotel]]s
*[[Landing platform dock]]s
*Maritime research
*[[Minesweeper (ship)|Mine sweepers]]
*[[Pipe-laying ship]]
*[[Platform supply vessel]]s
*[[Rock-dumping vessels|Rock dumping]]
*[[Sea Launch]]
*[[Sea-based X-band radar]]
*[[Shuttle tanker]]s
*[[Survey ship]]s

== Scope ==
A ship's motion can be described in terms of six [[Degrees of freedom (engineering)|degrees of freedom]], consisting of translation and rotation along three perpendicular axes.

The three translational motions are:
* '''Surge''': movement along the longitudinal axis (forward/astern)
* '''Sway''': movement along the lateral axis (starboard/port)
* '''Heave''': movement along the vertical axis (up/down)

The three rotational motions are:
* '''Roll''': rotation about the longitudinal axis
* '''Pitch''': rotation about the lateral axis
* '''Yaw''': rotation about the vertical axis

Dynamic positioning is primarily concerned with controlling a vessel in the [[horizontal plane]], namely translation along the two horizontal axes (surge and sway) and rotation about the vertical axis (yaw).

== Requirements ==
For a vessel to operate with dynamic positioning (DP), several essential components are required:
* '''Position and heading information''': Accurate knowledge of the ship's location and orientation is the foundation of DP.
* '''Control system''': A dedicated computer continuously calculates the corrective actions needed to maintain position and heading.
* '''Thrust elements''': Propellers and thrusters apply the forces demanded by the control system to counteract environmental influences.

When designing a DP vessel, careful consideration must be given to both the position reference systems and the available thrust. In particular, maintaining control in adverse weather requires sufficient thrust capability in all three axes of movement.

Maintaining a fixed position is especially challenging in [[Polar region|polar]] conditions, where [[Sea ice|ice]] forces can change rapidly. Current ship-borne ice detection and mitigation technologies are not yet advanced enough to predict these forces reliably, though they may offer advantages over sensors deployed by [[helicopter]].<ref name="Forskning" />

==Positioning systems==
{{further|Geopositioning}}

There are several means to determine a ship's position at sea. Most traditional methods used for ships navigation are not accurate enough for some modern requirements. For that reason, several [[positioning system]]s have been developed during the past decades. Producers of DP systems are: Marine Technologies LLC, [[Kongsberg Maritime]], [[Navis Engineering Oy]], [[GE]], [[SIREHNA (company)|SIREHNA]], [[Wärtsilä]] (ex L-3), MT-div. Chouest,{{typo help inline|date=March 2019}} [[Rolls-Royce plc]], [[Praxis Automation Technology]], Brunvoll AS. The term '''digital anchor''' has been used to describe such dynamic positioning systems.<ref>{{cite web |url=https://mercurymarine-gsdesign1.netdna-ssl.com/media/filer_public/eb/69/eb69ed99-8eec-4a3b-8fff-1b564fef577a/skyhook_digital_anchor_sell_sheet.pdf |title=Advertisement from Mercury Marine |access-date=2015-05-22 |archive-date=2015-05-22 |archive-url=https://web.archive.org/web/20150522111249/https://mercurymarine-gsdesign1.netdna-ssl.com/media/filer_public/eb/69/eb69ed99-8eec-4a3b-8fff-1b564fef577a/skyhook_digital_anchor_sell_sheet.pdf |url-status=dead }}</ref> The applications and availability depends on the type of work and water depth. The most common position reference systems (PRS) and position measuring systems (PME) are:

[[File:GPS Satellite NASA art-iif.jpg|thumb|[[GPS]] satellite in orbit]]
*'''[[DGPS]], Differential [[Global Positioning System|GPS]]'''. The position obtained by GPS is not accurate enough for use by DP. The position is improved by use of a fixed ground-based reference station (differential station) that compares the GPS position to the known position of the station. The correction is sent to the DGPS receiver by long wave radio frequency. For use in DP an even higher accuracy and reliability is needed. Companies such as Veripos, [[Fugro]] or C-Nav supply differential signals via satellite, enabling the combination of several differential stations. The advantage of DGPS is that it is almost always available. Disadvantages include degradation of the signal by ionospheric or atmospheric disturbances, blockage of satellites by cranes or structures and deterioration of the signal at high altitudes.<ref name="IMCA M141" /> There are also systems installed on vessels that use various [[GNSS augmentation|augmentation]] systems, as well as combining GPS position with [[GLONASS]].<ref name="Veripos" />
*'''Acoustics'''. This system consists of one or more [[transponders]] placed on the seabed and a [[transducer]] placed in the ship's hull. The transducer sends an acoustic signal (by means of [[Piezoelectricity|piezoelectric]] elements) to the transponder, which is triggered to reply. As the velocity of sound through water is known (preferably a soundprofile is taken regularly), the distance is known. Because there are many elements on the transducer, the direction of the signal from the transponder can be determined. Now the position of the ship relative to the transponder can be calculated. Disadvantages are the vulnerability to noise by thrusters or other acoustic systems. The use is limited in shallow waters because of ray bending that occurs when sound travels through water horizontally. Three types of HPR systems are commonly used:
**'''Ultra- or super- short base line, USBL or SSBL'''. This works as described above. Because the angle to the transponder is measured, a correction needs to be made for the ship's roll and pitch. These are determined by Motion Reference Units. Because of the nature of [[angle]] measurement, the accuracy deteriorates with increasing water depth.
**'''Long base line, LBL'''. This consists of an array of at least three transponders. The initial position of the transponders is determined by USBL and/ or by measuring the baselines between the transponders. Once that is done, only the ranges to the transponders need to be measured to determine a relative position. The position should theoretically be located at the intersection of imaginary spheres, one around each transponder, with a radius equal to the time between transmission and reception multiplied by the speed of sound through water. Because angle measurement is not necessary, the accuracy in large water depths is better than USBL.
**'''Short baseline, SBL'''. This works with an array of transducers in the ship's hull. These determine their position to a transponder, so a solution is found in the same way as with LBL. As the array is located on the ship, it needs to be corrected for roll and pitch.<ref name="IMCA M151" />
*'''Riser Angle Monitoring'''. On drillships, riser angle monitoring can be fed into the DP system. It may be an electrical [[inclinometer]] or based on USBL, where a riser angle monitoring transponder is fitted to the riser and a remote inclinometer unit is installed on the Blow Out Preventer (BOP) and interrogated through the ship's HPR.

[[File:Light Taut Wire.JPG|thumb|Light taut wire on the ''HOS Achiever'']]
*'''Light taut wire, LTW or LWTW'''. The oldest position reference system used for DP is still very accurate in relatively shallow water. A clumpweight is lowered to the seabed. By measuring the amount of wire paid out and the angle of the wire by a [[gimbal]] head, the relative position can be calculated. Care should be taken not to let the wire angle become too large to avoid dragging. For deeper water the system is less favourable, as current will curve the wire. There are however systems that counteract this with a gimbal head on the clumpweight. Horizontal LTW's are also used when operating close to a structure. Objects falling on the wire are a risk here.
*'''Fanbeam''' and '''CyScan'''. These are laser based position reference systems. They are very straightforward system, as only a prism cluster or tape target needs to be installed on a nearby structure or ship. Risks are the system locking on other reflecting objects and blocking of the signal. However, the Cyscan Absolute Signature which was released in 2017 was launched to address this issue. It is able to engage in an active lock with the Absolute Signature prism which reduces the chance of a wrong target being tracked. Range depends on the weather, but is typically more than 500 meters. New advancement, borrowed from the autonomous vehicle industry, are leading to the introduction of target-less PRS using fast laser scanners then Simultaneously Locating And Mapping (SLAM) one scan to the next to work out the relative movement of the vessel. Guidance Marine introduced the '''SceneScan''', a 2D scanner, in 2018. Furlong Sensing introduced the '''Unity''', a 3D scanner in 2025. As these target-less technologies mature it may be expected that solutions requiring installed targets will be retired. The offshore wind farm industry is leading the way as adding targets to many wind towers is a cost that can now be avoided.
*'''Artemis'''. A radar-based system. A unit is placed on a fixed station (FPSO) and the unit on board the mobile station locks on to it to report the range and bearing. The operational range is in excess of 4 kilometers. Advantage is the reliable, all-weather performance. Disadvantage is that the unit is rather heavy and costly. Current version is the Artemis Mk6.<ref name="IMCA M174" />
*'''DARPS, Differential, Absolute and Relative Positioning System'''. Commonly used on shuttle tankers while loading from a [[Floating Production Storage and Offloading|FPSO]]. Both will have a GPS receiver. As the errors are the same for the both of them, the signal does not need to be corrected. The position from the FPSO is transmitted to the shuttle tanker, so a range and bearing can be calculated and fed into the DP system.
*'''RADius'''<ref name="RADius" /> and '''RadaScan'''. These are radar based systems; while the RADius has no moving parts, the RadaScan has a rotating antenna under the dome. Guidance Marine has improved the miniRadaScan with the RadaScan View which has an added advantage of radar back-scatter.{{clarify|reason=How does radar back-scatter provide an advantage|date=September 2019}} This enhanced the DPO's situational awareness.{{clarify|how does this enhance the DPO's situational awareness?|date=March 2022}} These systems usually have responders which are active targets that send the signal back to the sensor to report the range and bearing. The range is typically up to 600 meters.{{cn|date=September 2019}}
*'''[[Inertial navigation]]''' is used in combination with any of the above reference systems, but typically with gnss (Global Navigation Satellite System) and Hydroacoustics (USBL, LBL, or SBL).

===Heading systems===
*'''[[Gyrocompass]]es''' are normally used to determine heading.

More advanced methods are:
*'''[[Ring laser gyro|Ring-Laser gyroscopes]]'''
*'''[[Fibre optic gyroscope]]s'''
*'''Seapath''', a combination of GPS and inertial sensors.

===Other sensors===
Besides position and heading, other variables are fed into the DP system through [[sensor]]s:
*'''[[Inertial measurement unit|Motion reference units, vertical reference units or vertical reference sensors]], VRUs or MRUs or VRSs''', determine the ship's roll, pitch and heave.
*'''[[Anemometer|Wind sensors]]''' are fed into the DP system [[Feed forward (control)|feedforward]], so the system can anticipate wind gusts before the ship is blown off position.
*'''[[Draft (nautical)|Draught]] sensors''', since a change of draught influences the effect of wind and [[Ocean current|current]] on the hull.
*Other sensors depend on the kind of ship. A pipelay ship may measure the force needed to pull on the pipe, large crane vessels will have sensors to determine the cranes position, as this changes the wind model, enabling the calculation of a more accurate model (see Control systems).
*Some external forces are not directly measured. In these cases, the offset force is deduced over a period of time, allowing an average value of compensating thrust to be applied. All forces not attributable to direct measurement are labeled "current", as this is what they are assumed to be, but in reality this is a combination of current, waves, swell, and any errors in the system. As is traditional in the maritime industry, DP "current" is always recorded in the direction that it is flowing towards.

==Control systems==
[[Image:Control-Kalman.svg|thumb|Block diagram of control system]]
In the beginning [[PID controller]]s were used and today are still used in the simpler DP systems. But modern controllers use a [[mathematical model]] of the ship that is based on a [[Hydrodynamics|hydrodynamic]] and [[aerodynamic]] description concerning some of the ship's characteristics such as [[mass]] and [[Drag (physics)|drag]]. Of course, this model is not entirely correct. The ship's position and heading are fed into the system and compared with the prediction made by the model. This difference is used to update the model by using [[Kalman filter]]ing technique. For this reason, the model also has input from the wind sensors and feedback from the thrusters. This method even allows not having input from any PRS for some time, depending on the quality of the model and the weather. This process is known as [[dead reckoning]].

The [[accuracy and precision]] of the different PRSs is not the same. While a DGPS has a high accuracy and precision, a USBL can have a much lower precision. For this reason, the PRS's are weighted. Based on [[variance]] a PRS receives a weight between 0 and 1.

==Power and propulsion systems==
[[image:North Sea Giant offshore installation vessel.jpg|thumb|North Sea Giant]]
To maintain position [[azimuth thruster]]s (electric, [[L-drive]] or [[Z-drive]]) [[bow thruster]]s, stern thrusters, [[Pump-jet|water jets]], [[rudder]]s and [[propeller]]s are used. DP ships are usually at least partially [[Diesel-electric transmission|diesel-electric]], as this allows a more flexible set-up and is better able to handle the large changes in power demand, typical for DP operations. These fluctuations may be suitable for [[Hybrid electric vehicle#Marine and other aquatic|hybrid operation]]. An [[Liquefied natural gas|LNG]]-powered platform supply vessel started operation in 2016 with a 653 kWh/1600&nbsp;kW [[battery pack|battery]] acting as [[Operating reserve|spinning reserve]] during DP2, saving 15-30% fuel.<ref name="Battery" /> The 154-meter North Sea Giant has combined 3 powerpacks, switchboards and 2 MWh batteries to operate in DP3 using only one engine,<ref>{{cite web |last1=Stensvold |first1=Tore |title=Et av verdens mest avanserte skip er bygget om: Sparer 30 prosent drivstoff med batteri |url=https://www.tu.no/artikler/et-av-verdens-mest-avanserte-skip-er-bygget-om-sparer-30-prosent-drivstoff-med-batteri/432656?key=17JN041I |website=Tu.no |publisher=[[Teknisk Ukeblad]] |access-date=31 March 2019 |language=no |date=14 March 2018}}</ref><ref>{{cite web |title=The Motorship {{!}} Giant battery boost for North Sea Shipping |url=https://www.motorship.com/news101/ships-equipment/giant-battery-boost-for-north-sea-shipping |website=www.motorship.com |access-date=31 March 2019}}</ref> keeping the engine load between 60% and 80%.<ref>{{cite web |last1=Førde |first1=Thomas |title=Dette fartøyet sparer penger og kutter CO2 med avansert batterisystem |url=https://www.tu.no/artikler/dette-fartoyet-sparer-penger-og-kutter-co2-med-avansert-batterisystem/465783 |website=Tu.no |publisher=[[Teknisk Ukeblad]] |language=no |date=31 May 2019}}</ref>

The set-up depends on the DP class of the ship. A Class 1 can be relatively simple, whereas the system of a Class 3 ship is quite complex. On Class 2 and 3 ships, all computers and reference systems should be powered through a [[Uninterruptible power supply|UPS]].

==International Maritime Organization class requirements==
Based on [[International Maritime Organization|IMO]] (International Maritime Organization) publication 645<ref name="IMO 645" /> the [[Classification Society|Classification Societies]] have issued rules for Dynamic Positioned Ships described as Class 1, Class 2 and Class 3.

*Equipment Class 1 has no redundancy.<br />Loss of position may occur in the event of a single fault.
*Equipment Class 2 has redundancy so that no single fault in an active system will cause the system to fail.<br />Loss of position should not occur from a single fault of an active component or system such as generators, thruster, switchboards, remote controlled valves etc., but may occur after failure of a static component such as cables, pipes, manual valves etc.
*Equipment Class 3 which also has to withstand fire or flood in any one compartment without the system failing.<br />Loss of position should not occur from any single failure including a completely burnt fire subdivision or flooded watertight compartment.

Classification Societies have their own Class notations:

{| class="wikitable"
|- valign="top"
|style="background:#DDDDDD"| Description ||style="background:#DDDDDD"| [[International Maritime Organization|IMO]]<br />Equipment Class||style="background:#DDDDDD"| [[Lloyd's Register|LR]]<br />Equipment Class ||style="background:#DDDDDD"| [[Det Norske Veritas|DNV]]<br />Equipment Class ||style="background:#DDDDDD"| [[Germanischer Lloyd|GL]]<br />Equipment Class||style="background:#DDDDDD"| [[American Bureau of Shipping|ABS]]<br />Equipment Class||style="background:#DDDDDD"| [[Nippon Kaiji Kyokai|NK]]<br />Equipment Class||style="background:#DDDDDD"| [[Bureau Veritas|BV]]<br />Equipment Class
|-
| style="background:#DDDDDD"| Manual position control and automatic heading control under specified maximum environmental conditions || - || DP(CM) || DYNPOS-AUTS || - || DPS-0 || -
|-
|- valign="top"
| style="background:#DDDDDD"| Automatic and manual position and heading control under specified maximum environmental conditions || Class 1 || DP(AM) || DYNPOS-AUT & DPS1|| DP 1 || DPS-1 || DPS A || DYNAPOS AM/AT
|-
|- valign="top"
| style="background:#DDDDDD"| Automatic and manual position and heading control under specified maximum environmental conditions, during and following any single fault excluding loss of a compartment. (Two independent computer systems). || Class 2 || DP(AA) || DYNPOS-AUTR & DPS2 || DP 2 || DPS-2 || DPS B || DYNAPOS AM/AT R
|-
|- valign="top"
| style="background:#DDDDDD"| Automatic and manual position and heading control under specified maximum environmental conditions, during and following any single fault including loss of a compartment due to fire or flood. (At least two independent computer systems with a separate backup system separated by A60 class division). || Class 3 || DP(AAA) || DYNPOS-AUTRO & DPS3 || DP 3 || DPS-3 || DPS C || DYNAPOS AM/AT RS
|}
DNV rules 2011 Pt6 Ch7 introduced "DPS" series of classification to compete with ABS "DPS" series.

==Norwegian Maritime Authority Guidelines==
Where IMO leaves the decision of which class applies to what kind of operation to the operator of the DP ship and its client, the [[Norwegian Maritime Authority]] (NMA) has specified what Class should be used in regard to the risk of an operation. In the NMA Guidelines and Notes No. 28, enclosure A four classes are defined:

*Class 0 Operations where loss of position keeping capability is not considered to endanger human lives, or cause damage.
*Class 1 Operations where loss of position keeping capability may cause damage or pollution of small consequence.
*Class 2 Operations where loss of position keeping capability may cause personnel injury, pollution, or damage with large economic consequences.
*Class 3 Operations where loss of position keeping capability may cause fatal accidents, or severe pollution or damage with major economic consequences.

Based on this the type of ship is specified for each operation:
*Class 1 DP units with equipment class 1 should be used during operations where loss of position is not considered to endanger human lives, cause significant damage or cause more than minimal pollution.
*Class 2 DP units with equipment class 2 should be used during operations where loss of position could cause personnel injury, pollution or damage with great economic consequences.
*Class 3 DP units with equipment class 3 should be used during operations where loss of position could cause fatal accidents, severe pollution or damage with major economic consequences.

==Failure ==
Loss of position, also known as runoff, can be a threat to safe operations and the environment, including possible loss of life, injury, damage to property or the environment, and loss of reputation and time. Incident records indicate that even vessels with redundant dynamic positioning systems are subject to occasional loss of position, which can be due to human error, procedural failure, dynamic positioning system failures, or bad design.<ref name="Castro 2015" /> 
{{expand section|date=November 2018}}

Dynamic positioning failure results in an inability to maintain position or heading control, and can be a drift off caused by insufficient thrust, or a drive off caused by inappropriate thrust.<ref name="Castro 2015" />

*Risk of runoff
*Consequences – for drilling, diving and other operations. Injury to divers is possible, Damage to diving equipment including cutting of diver's umbilical has occurred.<ref name="CADC" />
*Mitigation – dealing with a runoff; training and competence; emergency drills.<ref name="Castro 2015" />

===Dynamic positioning alarm and runout response for bell divers===
*Code amber / Yellow alert – Divers return to the bell immediately, stow umbilicals, and stand by for further developments and instructions.<ref name="IMCA D022 2016 11.8" />
*Code red – Divers return to the bell without delaying to retrieve tools and prepare for immediate ascent. The bell can not be recovered until the umbilicals have been safely stowed.<ref name="IMCA D022 2016 11.8" />
The basic response with a closed bell is similar to wet bell, but after stowing umbilicals, the hatch will be sealed so that internal pressure can be retained. The bell will be recovered as rapidly as possible in a red alert, and may be recovered if there is doubt that a yellow alert will be downgraded.<ref name="IMCA D022 2016 13.10" />

===Redundancy===
[[Redundancy (engineering)|Redundancy]] is the ability to withstand, while on DP mode, the loss of equipment which is online, without losing position or heading. A single failure can be, amongst others:
*Thruster failure
*Generator (power supply) failure
*[[Power bus]] failure (when generators are combined on one power bus)
*Control computer failure
*Position reference system failure
*Reference system failure{{clarify|date=March 2022}}

For certain operations redundancy is not required. For instance, if a survey ship loses its DP capability, there is normally no risk of damage or injuries. These operations will normally be done in Class 1.

For other operations, such as diving and heavy lifting, there is a risk of damage or injuries. Depending on the risk, the operation is done in Class 2 or 3. This means at least three Position reference systems should be selected. This allows the principle of voting logic, so the failing PRS can be found. For this reason, there are also three DP control computers, three gyrocompasses, three MRU's and three wind sensors on Class 3 ships. If a single fault occurs that jeopardizes the redundancy, i.e., failing of a thruster, generator or a PRS, and this cannot be resolved immediately, the operation should be abandoned as quickly as possible.

To have sufficient redundancy, enough generators and thrusters should be on-line so the failure of one does not result in a loss of position. This is left to the judgment of the DP operator. For Class 2 and Class 3 a [[Consequence Analysis]] should be incorporated in the system to assist the DPO in this process.

The redundancy of a DP ship should be judged by a [[Failure mode and effects analysis|failure mode and effects analysis (FMEA)]] study and proved by FMEA trials.<ref name="IMCA M166" /> Besides that, annual trials are done and normally DP function tests are completed prior to each project.

==DP operator==
The DP operator (DPO) judges whether there is enough redundancy available at any given moment of the operation. IMO issued MSC/Circ.738 (Guidelines for dynamic positioning system (DP) operator training) on 24-06-1996. This refers to IMCA (International Marine Contractors Association) M 117<ref name="IMCA M117" /> as acceptable standard.

To qualify as a DP operator the following path should be followed:
#a DP Induction course + On-line Examination
#a minimum of 60 days seagoing DP familiarisation
#a DP Advanced course + On-line Examination
#a minimum of 60 days watchkeeping on a DP ship
#a statement of suitability by the master of a DP ship

When the watchkeeping is done on a Class 1 DP ship, a limited certificate will be issued; otherwise a full certificate will be issued.

The DP training and certification scheme is operated by The Nautical Institute (NI). The NI issue logbooks to trainees, they accredit training centres and control the issuance of certification.

With ever more DP ships and with increasing manpower demands, the position of DPO is gaining increasing prominence. This shifting landscape led to the creation of The International Dynamic Positioning Operators Association (IDPOA) in 2009. www.dpoperators.org

IDPOA membership is made up of certified DPO's who qualify for fellowship (fDPO), while Members (mDPO) are those with DP experience or who may already be working within the DP certification scheme.

==International Marine Contractors Association==
The [[International Marine Contractors Association]] was formed in April 1995 from the amalgamation of the Dynamic Positioning Vessel Owners Association, founded in 1990, and the International Association of Offshore Diving Contractors, founded in 1972.<ref name="IMCA DP History" />

While it started with the collection and analysis of DP Incidents,<ref name="IMC M181" /> since then it has produced publications on different subjects to improve standards for DP systems. It also works with IMO and other regulatory bodies.

== Marine Technology Society Dynamic Positioning Committee ==
The [[Marine Technology Society]] Dynamic Positioning (DP) Committee's mission is to facilitate incident free DP operations through sharing of knowledge. This committee of dedicated volunteers delivers value to the DP community of vessel owners, operators, Marine Class Societies, engineers and regulators through an annual DP Conference, topical workshops and an extensive set of Guidance Documents covering DP Design Philosophy, DP Operations and Professional Development of DP Personnel. In addition, a growing set of unique documents called TECHOP's address specific topics of significant interest and impact. Conference papers are available for download by the public, providing the most comprehensive single source of DP industry technical papers available anywhere.

The DP Guidance documents published by the MTS DP Committee are designed to disseminate the knowledge, methods and unique tools to aid the DP community in achieving incident free DP operations. The documents are free to download from the Committee's website http://dynamic-positioning.com

== See also ==
* {{annotated link|Autonomous spaceport drone ship}}
* {{annotated link|Autopilot}}
<!--* [[Mercury Skyhook]], Mercury Marine [[Skyhook (cable)|Skyhook]] [[Digital anchor|Digital Anchor]] for outboard motor boats uses GPS and electronic compass to lock position and heading for dynamic positioning against wind and tide.-->
*[[Last Breath (2019 film)]] – 2019 documentary about a dynamic positioning failure that led to a serious accident, a severed umbilical, and the near loss of a diver

== References ==
{{Reflist|refs=

<ref name="Battery">{{cite web|url= http://www.tu.no/artikler/forste-i-verden-her-skal-batterier-erstatte-motor-i-kritiske-situasjoner/359157 |title=Første i verden: Her skal batterier erstatte motor i kritiske situasjoner|work=[[Teknisk Ukeblad]] |last=Stensvold |first=Tore |access-date=11 October 2016|publisher=Teknisk Ukeblad Media AS |date=2016-10-11}}</ref>

<ref name="CADC">{{cite web |url=http://cadc.ca/blog/2012/10/dynamically-positioned-vessel-run-off-severance-of-bell-divers-umbilical/ |title=Dynamically Positioned Vessel Run-off / Severance of Bell Diver's Umbilical |publisher=Canadian Association of Diving Contractors |date=31 October 2012 |author= CADC Admin |access-date=29 November 2018}}</ref>

<ref name="Castro 2015">{{cite conference |url=https://dynamic-positioning.com/proceedings/dp2015/Training_Castro_2015.pdf |title=DP Emergency Drills |last= Castro |first=Alexander |conference=Dynamic Positioning Conference|publisher=Marine Technology Society |location=Houston |date= 13–14 October 2015 }}</ref>

<ref name="Forskning">{{cite web|url= https://www.tu.no/artikler/forskning-systemet-skal-muliggjore-kompliserte-operasjoner-i-is-og-ekstremvaer/375918 |title=Forskning: Dynamisk Posisjonering for Arktis: Systemet skal muliggjøre kompliserte operasjoner i is og ekstremvær|work=[[Teknisk Ukeblad]] |access-date=2 February 2017|date=February 2017 |first=Grete |last=Wolden }}</ref>

<ref name="IMCA D022 2016 11.8">{{harvnb|Guidance for diving supervisors IMCA D 022|loc=chpt. 11 Surface supplied air diving, sect. 8 Emergency and contingency plans}}</ref>

<ref name="IMCA D022 2016 13.10">{{harvnb|Guidance for diving supervisors IMCA D 022|loc=chpt. 13 Closed bell diving, sect. 10 Emergency and contingency plans}}</ref>

<ref name="IMCA DP History">{{cite web | url = http://www.imca-int.com/documents/core/imca/promotion/IMCA-MarineDPHistory.pdf | title = Dynamiv positioning - A brief IMCA History | url-status = dead | archive-url = https://web.archive.org/web/20060311134453/http://www.imca-int.com/documents/core/imca/promotion/IMCA-MarineDPHistory.pdf | archive-date = 2006-03-11 |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="IMCA M117">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/117.html | title = IMCA M 117, The training and experience of key DP personnel |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="IMCA M141">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/141.html | title = IMCA M 141, Guidelines on the Use of DGPS as a Position Reference in DP Control Systems |publisher=International Marine Contractors Association |location=London |date=October 1997}}</ref>

<ref name="IMCA M151">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/151.html | title = IMCA M 151, The Basic Principles and Use of Hydroacoustic Position Reference Systems in the Offshore Environment |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="IMCA M166">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/166.html | title = IMCA M 166, Guidelines on Failure Modes & Effects Analyses (FMEAs) |publisher=International Marine Contractors Association |location=London }}</ref>

<!--
<ref name="IMCA M170">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/170.html | title = IMCA M 170, A Review of Marine Laser Positioning Systems}}</ref>
-->

<ref name="IMCA M174">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/174.html | title = IMCA M 174, A Review of the Artemis Mk V Positioning System |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="IMC M181">{{cite web | url = http://www.imca-int.com/divisions/marine/publications/181.html | title = IMCA M 181, Analysis of Station Keeping Incident Data 1994-2003 |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="IMO 645">{{cite web | url = http://www.imo.org/includes/blastDataOnly.asp/data_id%3D10015/MSCcirc645.pdf | archive-url = https://web.archive.org/web/20070610161824/http://www.imo.org/includes/blastDataOnly.asp/data_id%3D10015/MSCcirc645.pdf | url-status = dead | archive-date = 2007-06-10 | title = IMO MSC/Circ.645, Guidelines for vessels with dynamic positioning systems |date=6 June 1994}}</ref>

<ref name=Intro>[http://www.imca-int.com/divisions/marine/reference/intro01.html Introduction to Dynamic Positioning] {{webarchive|url=https://web.archive.org/web/20100626080452/http://www.imca-int.com/divisions/marine/reference/intro01.html |date=2010-06-26 |publisher=International Marine Contractors Association |location=London }}</ref>

<ref name="Nautinst">{{Cite web |url=http://www.nautinst.org/en/dynamic-positioning/what-is-dynamic-positioning/index.cfm |title=What is dynamic positioning? |access-date=2013-01-24 |archive-url=https://web.archive.org/web/20130125101320/http://www.nautinst.org/en/dynamic-positioning/what-is-dynamic-positioning/index.cfm |archive-date=2013-01-25 |url-status=dead |publisher=The Nautical Institute}}</ref>

<ref name="RADius">{{cite web | url = https://www.youtube.com/watch?v=79f4g-Gyl5E | title = RADius relative positioning system |publisher=Konsberg Gruppen |date=15 August 2011}}</ref>

<ref name="Veripos">{{cite web | url = http://www.veripos.com/s_ultra.php | title = Veripos DP system can be installed with several Augmentation systems as well as GLONASS support, they can disable any satellite or service via Ultra corrections received via Spotbeam or Inmarsat links. | url-status = dead | archive-url = https://archive.today/20060525215827/http://www.veripos.com/s_ultra.php | archive-date = 2006-05-25 }}</ref>

}}

===Sources===
* {{cite book|last=Staff|title=Guidance for diving supervisors IMCA D 022|edition=Revision 1|date=August 2016|publisher=International Marine Contractors Association|location=London, UK|ref={{sfnRef|Guidance for diving supervisors IMCA D 022}} }}

==External links==
{{commons category|Dynamic positioning}}
*[http://myship.com/all-offshore-vessels List of all offshore vessels]
*[http://www.imo.org IMO, International Maritime Organization]
*[https://web.archive.org/web/20051226225736/http://www.imca-int.com/divisions/marine/reference/intro.html Introduction to Dynamic Positioning] by the International Marine Contractors Association (IMCA)
*[https://web.archive.org/web/20060222204951/http://www.sjofartsdir.no/english.asp NMD, Norwegian Maritime Directorate]
*[https://web.archive.org/web/20060326102525/http://www.oilpubs.com/v_catalog/homewelcome.asp?orderdetail=69 OPL Oilfield Seamanship Series - Volume 9: Dynamic Positioning - 2nd Edition] by David Bray
*[http://www.nautinst.org NI, The Nautical Institute]
*[http://www.dynamic-positioning.com/ The Dynamic Positioning Committee of The Marine Technology Society]
*[http://www.dpoperators.org The International Dynamic Positioning Operators Association (IDPOA)]

{{DEFAULTSORT:Dynamic Positioning}}
[[Category:Navigational equipment]]
[[Category:Offshore engineering]]
[[Category:Geopositioning]]