Offshore Support Vessel Toisa Perseus with, in the background, the fifth-generation deepwater drillship Discoverer Enterprise, at the Thunder Horse location. A drillship is a maritime vessel that has been fitted with drilling apparatus Thunder Horse is the largest moored Semi-submersible Oil platform in the world located in 1920 metres (6300 ft of water in Both are equipped with DP systems.

Dynamic positioning (DP) is a computer controlled system to automatically maintain a ship’s position and heading by using her own propellers and thrusters. A ship /ʃɪp/ is a large vessel that floats on water Ships are generally distinguished from Boats based on size Position reference sensors, combined with wind sensors, motion sensors and gyro compasses, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. A gyrocompass is similar to a Gyroscope. It is a Compass that finds True north by using an (electrically powered fast-spinning wheel and friction

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 favourable angle towards wind, waves and current, called weathervaning.

Dynamic positioning is much used in the offshore oil industry, for example in the North Sea, Persian Gulf, Gulf of Mexico, West Africa and off Brazil. The North Sea is a marginal, Epeiric sea of the Atlantic Ocean on the European Continental shelf. The Persian Gulf, in the Southwest Asian region is an extension of the The Gulf of Mexico ( Spanish: Golfo de México) is the ninth largest Body of water in the world West Africa or Western Africa is the Westernmost Region of the African Continent. |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld Nowadays there are more than 1000 DP ships.

History

Dynamic positioning started in the 1960’s for offshore drilling. With drilling moving into ever deeper waters, Jack-up barges could not be used any more and anchoring became less economical. A jack-up rig is a type of mobile offshore oil and gas drilling platform that is able to stand still on the sea floor, resting on a number of supporting legs

Cuss 1

In 1961 the drillship Cuss 1 was fitted with four steerable propellers, in an attempt to drill the first Moho well. The Mohorovičić discontinuity, usually referred to as the Moho, is the boundary between the Earth 's crust and the mantle. It was possible to keep the ship in position above the well off La Jolla, California, at a depth of 948 meter.

After this, off the coast of Guadalupe, Mexico, five holes were drilled, the deepest at 183 m (601 ft) below the sea floor in 3,500 m (11,700 ft) of water, while maintaining a position within a radius of 180 meter. The ship's position was determined by radar ranging to buoys and sonar ranging from subsea beacons. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships

Whereas the Cuss 1 was kept in position manually, later in the same year Shell launched the drilling ship Eureka that had an analogue control system interfaced with a taut wire, making it the first true DP ship. Shell Oil Company is the United States -based affiliate of Royal Dutch Shell, a multinational oil company (" Oil major " of Anglo

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 any more, but on various other types of ships. In addition, DP is not limited to maintaining a fixed position any more. One of the possibilities is sailing an exact track, useful for 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. An anchor is an object often made out of metal that is used to attach a ship to the bottom of a body of water at a specific point All have their own advantages and disadvantages.

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

SBX underway

Important applications include:

• Servicing Aids to Navigation (ATON)
• Cable-laying
• Crane vessels
• Cruise ships
• Diving support vessels
• Dredging
• Drillships
• FPSOs
• Flotels
• Landing Platform Docks
• Maritime research
• Mine sweepers
• Pipe-laying
• Platform supply vessels
• Rockdumping
• Sea Launch
• Sea-based X-band Radar
• Shuttle tankers
• Survey ships

Scope

A ship can be considered to have six degrees of freedom in its motion, i. Sea-Based X-Band Radar is a floating self-propelled mobile Radar station designed to operate in high winds and heavy seas navigational aid (also known as aid to navigation ATON or navaid) is any sort of marker which aids the traveler in navigation the term is most commonly navigational aid (also known as aid to navigation ATON or navaid) is any sort of marker which aids the traveler in navigation the term is most commonly A cable layer or cable ship is a deep-sea vessel designed and used to lay underwater cables for telecommunications electricity and such A crane vessel, crane ship or floating crane is a Ship that is specialized in lifting heavy loads A cruise ship or cruise liner is a Passenger ship used for pleasure voyages where the voyage itself and the ship's amenities are part of the experience A diving support vessel is a Ship that is used as a floating base for Professional diving projects Dredging is an Excavation activity or operation usually carried out at least partly underwater in shallow seas or Fresh water areas with the purpose of A drillship is a maritime vessel that has been fitted with drilling apparatus A Floating Production Storage and Offloading vessel ( FPSO; also called a "unit" and a "system" is a type of floating tank system used by the offshore Flotel, a Portmanteau of the terms '''flo'''ating ho'''tel''', refers to the installation of living quarters on top of Rafts An amphibious transport dock (also called a landing platform dock or LPD) is an Amphibious warfare ship, a warship that embarks transports and lands elements A minesweeper is a Naval Warship designed to counter the threat posed by Naval mines The dedicated purpose-built minesweeper first appeared during Sea-Based X-Band Radar is a floating self-propelled mobile Radar station designed to operate in high winds and heavy seas A shuttle tanker is a ship designed for oil transport from an off-shore Oil field. A research vessel (R/V is a Ship designed and equipped to carry out Research at Sea. In mechanics, degrees of freedom (DOF are the set of independent displacements and/or rotations that specify completely the displaced or deformed position and orientation e. it can move in any of six axes.

Three of these involve translation:

• surge (forward/astern)
• sway (starboard/port)
• heave (up/down)

and the other three rotation:

• roll (rotation about surge axis)
• pitch (rotation about sway axis)
• yaw (rotation about heave axis)

Dynamic positioning is concerned primarily with control of the ship in the horizontal plane, i. In Physics, translation is movement that changes the position of an object as opposed to Rotation. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation e. the three axis surge, sway and yaw.

Requirements

A ship that is to be used for DP requires:

• to maintain position and heading, first of all the position and heading need to be known.
• a control computer to calculate the required control actions to maintain position and correct for position errors. A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems
• thrust elements to apply forces to the ship as demanded by the control system.

For most applications, the position reference systems and thrust elements must be carefully considered when designing a DP ship. In particular, for good control of position in adverse weather, the thrust capability of the ship in three axes must be adequate. The main manufacturers of DP systems are Kongsberg Maritime, Converteam (formerly a part of Alstom), L-3 Communications (formerly Nautronix), Rolls-Royce Marine, Marine Technologies and Navis Engineering Oy. Kongsberg Maritime (KM is a Norwegian technology enterprise within the Kongsberg Gruppen (KOG Converteam is the power conversion company that formerly traded as Alstom Power Conversion Alstom ( is a large French multinational conglomerate which holds interests in the power generation and Transport markets Not to be confused with Level 3 Communications, an Internet carrier L-3 Communications Holdings Inc

Reference systems

Position reference systems

There are several means to determine a ship's position at sea. Most traditional methods used for ships navigation are not accurate enough. For that reason, several systems have been developed during the past decades. The availability depends on the type of work and water depth. The most common Position reference/Measuring systems /Equipment (PRS/PME) are:

GPS satellite in orbit.

• DGPS, Differential GPS. Differential Global Positioning System (DGPS is an enhancement to Global Positioning System that uses a network of fixed ground-based reference stations to broadcast the difference Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth 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 as Fugro supply differential signals via satellite, enabling the combination of several differential stations. Fugro NV is a Dutch multinational company headquartered in Leidschendam The advantage of DGPS is that it is almost always available. Disadvantages are degrading of the signal because of sunspots or atmospheric disturbances, blockage of satellites by cranes or structures and deterioration of the signal at high altitudes. ^[1]
• Hydroacoustic Position Reference, HPR. 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 piezoelectric elements) to the transponder, which is triggered to reply. Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to 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. Furthermore, 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. In Geometry and Trigonometry, an angle (in full plane angle) is the figure formed by two rays sharing a common Endpoint, called
  • 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. ^[2]
• 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. An inclinometer or clinometer is an instrument for measuring angles of Slope (or Tilt) Elevation or Inclination of an object with
• Light Taut Wire, LTW. The oldest position reference system used for DP is still very accurate in relative 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. A gimbal is a pivoted support that allows the rotation of an object about a single axis 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/ CyScan. Both are laser based position reference systems. A very straightforward system, as only a small prism needs to be installed on a nearby structure. Risks are the fanbeam locking on other reflecting objects and blocking of the signal. Range depends on the weather, but is typically more than 500 meters. CyScan has the added advantage of an Auto-Tilt mechanism which compensates for waves motion by the use of actuators and gyro's. ^[3]
• Artemis. A radar based system. A unit is placed on a nearby structure and aimed at the unit on board the ship. The range is several kilometres. Advantage is the reliable, all-weather performance. Disadvantage is that the unit is rather heavy. ^[4]
• DARPS, Differential, Absolute and Relative Positioning System. Commonly used on shuttle tankers while loading from a FPSO. A Floating Production Storage and Offloading vessel ( FPSO; also called a "unit" and a "system" is a type of floating tank system used by the offshore 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. The manufacturer is Kongsberg Seatex a subsidiary of Kongsberg Maritime.
• RADius. A radar based system, but no moving parts as Artemis. Another advantage is that the transponders are much smaller than the Artemis unit. The RADius range for tracking the transponders has improved from approx. 200 meters to more than 1100 meters introducing the new RADius 700 Transponder. The coverage is also improved from 90 degree to 360 degree using the new RADius Modular Extension SW. The manufacturer is Kongsberg Seatex a subsidiary of Kongsberg Maritime. Kongsberg Maritime (KM is a Norwegian technology enterprise within the Kongsberg Gruppen (KOG
• RadaScan. A radar based system similar to RADius. Advantage is the target tracking distance up to 1000 meter and 360 degree coverage.
• Inertial navigation is used in combination with GPS (Seapath) and Hydroacoustics (HAIN). An Inertial Navigation System (INS is a Navigation aid that uses a Computer and motion sensors to continuously track the position orientation and Velocity

Heading reference systems

• Gyrocompasses are normally used to determine heading. A gyrocompass is similar to a Gyroscope. It is a Compass that finds True north by using an (electrically powered fast-spinning wheel and friction

More advanced methods are:

• Ring-Laser gyroscopes
• Fibre optic gyroscopes
• Seapath, a combination of GPS and inertial sensors. A ring laser gyroscope (RLG uses Interference of Laser light within a optical ring to detect changes in orientation and spin A fibre optic gyroscope (FOG is a Gyroscope that uses the Interference of light to detect mechanical rotation

Reference systems

Besides position and heading, other variables are fed into the DP system through sensors:

• Motion Reference Units, Vertical Reference Units or Vertical Reference Sensors, VRU's or MRU's or VRS's, determine the ship's roll, pitch and heave. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument inertial guidance systemAn inertial measurement unit, or IMU is the main component of Inertial guidance systems used in air-, space-, and Watercraft
• Wind sensors are fed into the DP system feed-forward, so the system can anticipate wind gusts before the ship is blown off position. An anemometer is a device for measuring wind speed and is one instrument used in a Weather station. Feed-forward is a term describing a kind of System which reacts to changes in its environment usually to maintain some desired state of the system
• Draught sensors, since a change of draught influences the effect of wind and current on the hull. An ocean current is continuous directed movement of Ocean water.
• 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).

Control systems

In the beginning PID controllers were used and today are still used in the simpler DP systems. A proportional–integral–derivative controller (PID controller is a generic Control loop Feedback mechanism widely used in industrial Control systems But modern controllers use a mathematical model of the ship that is based on a hydrodynamic and aerodynamic description concerning some of the ship's characteristics such as mass and drag. Note The term model has a different meaning in Model theory, a branch of Mathematical logic. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a 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 filtering technique. The Kalman filter is an efficient Recursive filter that estimates the state of a Dynamic system from a series of noisy measurements For this reason, the model also has input from the windsensors 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.

The accuracy and precision of the different PRS’s 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 weighed. Based on variance a PRS receives a weight between 0 and 1. In Probability theory and Statistics, the variance of a Random variable, Probability distribution, or sample is one measure of

Power and propulsion systems

To maintain position azimuth thrusters (L-drive or Z-drive), azipods, bow thrusters, stern thrusters, water jets, rudders and propellors are used. An Azimuth thruster is a configuration of Ship propellers placed in pods that can be rotated in any horizontal direction making a Rudder unnecessary A L-drive is a type of Azimuth thruster in which the pod-mounted propellers are driven mechanically rather than electrically A Z-drive is a type of Azimuth thruster in which the pod-mounted propellers are driven mechanically rather than electrically Azipod is the registered Brand name of the ABB Group for their Azimuth thruster. A bow thruster, is a propulsion device built into or mounted to the bow of a Ship or Boat to enhance its maneuverability A pump-jet or water jet is a marine system that creates a jet of Water for propulsion. A rudder is a device used to steer a Ship, Boat, Submarine, Hovercraft, or other conveyance that move through a fluid (generally air or A propeller is essentially a type of fan which transmits power by converting Rotational motion into Thrust for propulsion of a vehicle such as an DP ships are usually at least partially 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. A number of vehicles use a diesel-electric Powertrain for providing locomotion.

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 UPS. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous

Class Requirements

Based on IMO (International Maritime Organization) publication 645^[5] the Classification Societies have issued rules for Dynamic Positioned Ships described as Class 1, Class 2 and Class 3. The International Maritime Organization ( IMO) formerly known as the Inter-Governmental Maritime Consultative Organization ( IMCO) is a late 20th century In the Shipping industry classification societies are Non-governmental organizations or groups of professionals Ship surveyors and representatives of offices

• Equipment Class 1 has no redundancy.
  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.
  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.
  Loss of position should not occur from any single failure including a completely burnt fire sub division or flooded watertight compartment.

Classification Societies have their own Class notations:

NMD

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 Directorate (NMD) has specified what Class should be used in regard to the risk of an operation. In the NMD 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.

Redundancy

Redundancy is the ability to cope with a single failure without loss of position. In Engineering, redundancy is the duplication of critical components of a system with the intention of increasing reliability of the System, usually A single failure can be, amongst others:

• Thruster failure
• Generator failure
• Powerbus failure (when generators are combined on one powerbus)
• Control computer failure
• Position reference system failure
• Reference system failure

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

Disadvantage is that a generator can never operate at full load, resulting in less economy and fouling of the engines.

The redundancy of a DP ship should be judged by a FMEA study and proved by FMEA trials^[6]. Besides that, annual trials are done and normally DP function tests are completed prior to each project.

DP Operator

The DP operator 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^[7] as acceptable standard.

To qualify as a DP operator the following path should be followed:

1. a DP Induction course
2. a minimum of 30 days seagoing DP familiarisation
3. a DP Advanced course
4. a minimum of 6 months watchkeeping on a DP ship
5. 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 Traning 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.

IMCA

The International Marine Contractors Association was formed in April 1995 from the amalgamation of AODC (originally the International Association of Offshore Diving Contractors), founded in 1972, and DPVOA (the Dynamic Positioning Vessel Owners Association), founded in 1990. ^[8] It represents offshore, marine and underwater engineering contractors. Acergy, Allseas, Heerema Marine Contractors, Helix Energy Solutions Group, Saipem, Subsea 7 and Technip have representation on IMCA's Council and provide the president. Previous presidents are:

• 1995-6 - Derek Leach, Coflexip Stena Offshore
• 1997-8 - Hein Mulder, Heerema Marine Contractors
• 1999/2000 - Donald Carmichael, Coflexip Stena Offshore
• 2001-2 - John Smith, Halliburton Subsea/Subsea 7
• 2003-4 - Steve Preston, - Heerema Marine Contractors
• 2005 - Frits Janmaat, Allseas Group

(2005 Vice-President - Knut Boe, Technip)

While it started with the collection and analysis of DP Incidents,^[9] since then it has produced publications on different subjects to improve DP standards. It also works with IMO and other regulatory bodies.

References

1. ^ IMCA M 141, Guidelines on the Use of DGPS as a Position Reference in DP Control Systems.
2. ^ IMCA M 151, The Basic Principles and Use of Hydroacoustic Position Reference Systems in the Offshore Environment.
3. ^ IMCA M 170, A Review of Marine Laser Positioning Systems.
4. ^ IMCA M 174, A Review of the Artemis Mk V Positioning System.
5. ^ IMO MSC/Circ.645, Guidelines for vessels with dynamic positioning systems.
6. ^ IMCA M 166, Guidelines on Failure Modes & Effects Analyses (FMEAs).
7. ^ IMCA M 117, The training and experience of key DP personnel.
8. ^ IMCA DP History.
9. ^ IMCA M 181, Analysis of Station Keeping Incident Data 1994-2003.

External links

• [http://www.thrustmastertexas.com/products/portableDynamicPositioningSystems.html The Thrustmaster Portable Dynamic Positioning System (PDPS) is a unique system for dynamic positioning of vessels, barges and floating structures of any size. Thrustmaster’s portable dynamic positioning systems facilitates affordable and quick dock-side conversion of any vessel to DP-0 thru DP-3 per any of the major classification societies.
• IMO, International Maritime Organization
• Introduction to Dynamic Positioning by the International Marine Contractors Association (IMCA)
• NMD, Norwegian Maritime Directorate
• OPL Oilfield Seamanship Series - Volume 9: Dynamic Positioning - 2nd Edition by David Bray
• NI, The Nautical Institute
• The Dynamic Positioning Committee of The Marine Technology Society