DP Systems

Dynamic Positioning systems allow a vessel to remain at a fixed point independent of

the influences of the environment. This is achieved by a system of reference points,
sensors and propulsive power units.
The reference points determine the vessels position relative to a datum, they do not
necessarily determine the vessels exact location on the earths surface- only DGPS
attempts to do this.
Sensors monitor the environmental effects on the vessel, such as the effects of swell
and wind and use this to error compensate the reference systems.
Propulsive power units take the form of the main propulsion unit, thrusters and
steering gear system ( in conjunction with propulsive unit). These units are mounted
for and aft and may be either fixed or steerable.
The number of reference systems, sensors and propulsion units is determined by the
required duties of the vessel

Types of reference systems

This is a non exhaustive list of the types of reference systems available;

 Differential GPS- The reliability of this system is very much dependent on the
location and can range from good to very poor
 Microwave (Artemis)- Is limited in that it is a line of site only system, the
advantage is that a communication link is available and emergency shut down
systems are sometimes built in
 Laser (Fanbeam)- This cheap reference can be initially very reliable reducing
as the target becomes dirty or due to atmospherics. It is a line of site reference
 Acoustic (HPR)-Can be reliable but is reliant on batteries in portable
transponders ( no limitation exists with fixed transponders)
 Taut Wire- Very reliable simple system. Can introduce movement restrictions
when in use.

Taut Wire
The wire passes through a Gimball head which is free to move in X and Y axis up to
the mechanical limitations of the assembly. The angle the head is at relative to the
vertical for the X axis and horizontal for the Y axis is measured by potentiometers and
sent to the DP computer. The wire length is measured by a line out counter and sent to
the DP computer. With the weight on the bottom contant tension is placed on the wire
keeping it taut, this is achieved by having a constant rpm electric motor coupled to the
wire drum via an electric clutch. The field current on the clutch determines the degree
of coupling and thereby the degree of torque ( note that this torque if far to small to
lift the weight and a seperate hydraulic motor is provided).

As the vessel moves the angle between the head and weight as well as the wire length
will alter. A calculation is made by the DP computer which gives the vessels relative
position to the weight. Vessel movement through wave action is measured by the
accelerometers and factored in.

Shown is a system which is deployed from the ships side, a limitation is placed on the
vessels movement towards the weight when the vessel is 'walked' ( say moving into
position or following an ROV). A second system would be mounted on the opposite
side. Alternately a single system may be fitted operating through a moonpool in the
centre of the vessel.

The size of the weight ( and corresponding wire diameter) is determined by the depth
that the vessel operates and the operating conditions the vessel works in. Typically
they would be not less than 350Kg

Described is a vertical taut wire system. Also available are horizontal taut wires which
give the same degree of reliability without the need for the clump weight. The
disadvantage is that they must be manually tethered.

Laser (fanbeam)

This is an auto tracking system whereby a scanning head fires a laser beam through
one lens and receives a reflecion of it through a second
The targets must be equiped with reflectors, reflective white tpae may be used but the
range is very limited. Greater distance is achieved prisms. 360' coverage is achieved
by mounting these prisms on a tube.

Position reference is by the laser ( this is a class one low power unit similar to that
found in CD players) scanning for the target. The bearing and range of the target is
found and by calculation using error correction from the vertical reference units the
movement between the two points is known.

Differential GPS
The GPS signal from a satellite does not give the degree of accuracy required for a
vessel positioning system. To improve accuracy differential GPS is used

A satellite signal is received by both the vessel and by an installation whose position
is precisely known. Any error in the signal from the satellite is converted into and
error correction signal which is then broadcast. This signal is received by the vessel, a
calculation is made and a more precise position now known.

This system is inherently risky for vessels working in critical positions and it is often
required that GPS be not used as both of the minimum two sources required. The gps
signal is sometimes intermittent as is the error compensation signal, they are effected
by reflection from nearby installations and by ionospheric variation. Multiple stations
are used to improve accuracy
Microwave (Artemis)

This consists of two stations. One unit mounted on a fixed installation, a second unit
mounted on the vessel. These units consist of a rotateing antenna. When initialised
both units rotate untill they point at each other. Manual control is available to speed
this up. Once they have acquired each other the antenna horns point continuously at
each other
The fixed unit now knows the relative postion of the vessel to itself by measurement
of the angle of the 'antenna relative to north. The microwave connection gives the
relative distance of the vessel. This information is given to the vessel. As the vessel
moves there will be alterations in the distance and the bearing between the units. An
error correction is made for changes in the ships heading measured by the GYRO.

Hydro Acoustic (HPR)

This system consists of an acoustic transponder and a sensor mounted on the vessel.
The transponder may be fixed to the sea bed or installation required , be lowered to
the sea bed as required from the vessel or be attached to a moving unit such as a diver
or ROV to allow the vessel to 'watch' the know their location.
The sensor may be fixed so that it looks in one direction only, or tracking where it can
move to locate several targets. To prevent interference from the vessels hull the
sensors are normally mounted on a long pole which may be lowered through an
isolation valve . The installation allows access to the sensor head for maintenance

The system is subject to variations in water temperature and salinity which effects the
sound velocity. At water stratification layers a degree of refraction occurs to the wave.

Sensors

Wind- This measures both the wind speed and wind direction. A calculation based on
parameters such as vessel topside area is made on the effect of the vessel. This signal
is fed forward to the DP Computer so that action may be taken before the vessel
moves off station

Gyro-Measures the vessels heading giving error correction for such reference systems
as artemis.

Vertical reference Unit-used to measure the vessels pitch and roll and used as error
corrections on such reference systems as taut wire, artemis etc.

Draught-Used on vessels such as heavy lift where ships operations may significantly
effect the draught of the vessel

Draghead Force-Used on dredges where the vessels forward speed is governed by the
loading of the draghead

There is generally no current measurement, instead the current is calculated by the DP

computer which looks for a permanent off set in the thrust required to keep the vessel
in position. Depending on the class of vessels all sensors may be duplicated

Dynamic positioning (DP) is a computer-controlled system to automatically maintain

a vessel's position and heading by using its own propellers and thrusters. 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. Examples of vessel types that
employ DP include, but are not limited to, ships and semi-submersible mobile offshore
drilling units (MODU), oceanographic research vessels, cable layer ships and cruise
ships.
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.[1]

History[edit]
Dynamic positioning began in the 1960s for offshore drilling. With drilling moving into
ever deeper waters, Jack-up barges could not be used any more, and anchoring in deep
water was not economical.
As part of Project Mohole, in 1961 the drillship Cuss 1 was fitted with four steerable
propellers. The Mohole project was attempting to drill to the 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, 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 meters. 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 launched
the drilling ship Eureka that had an analogue control system interfaced with a taut wire,
making it the first true DP ship.[2]
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 any more. One of the possibilities is sailing an exact track,
useful for cablelay, pipelay, survey and other tasks.

Comparison between position-keeping

options[edit]
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.

Comparison position-keeping options[2]

Dynamic positioning Anchoring Jack-up barge

Advantages: Advantages:
Advantages:
 Maneuverability is excellent;  No complex
it is easy to change position. systems with  No complex
 No anchor handling tugs are thrusters, extra systems with
required. generators and thrusters, extra
 Not dependent on water controllers. generators and
depth.  No chance of controllers.
 Quick set-up. running off position  No chance of
 Not limited by obstructed by system failures or running off position
seabed. blackouts. by system failures or
 No underwater blackouts.
hazards from  No underwater
thrusters. hazards from
 thrusters.
Disadvantages: Disadvantages: Disadvantages:

 Complex systems with  Limited  No maneuverability

thrusters, extra generators maneuverability once positioned.
and controllers. once anchored.  Limited to water
 High initial costs of  Anchor handling depths of 175
installation. tugs are required. meters.
 High fuel costs.  Less suitable in
 Chance of running off deep water.
position in case of strong  Time to anchor out
currents or winds, or due to varies between
system failures or blackouts. several hours to
 Underwater hazards from several days.
thrusters for divers  Limited by
and ROVs. obstructed seabed
 Higher maintenance of the (pipelines, seabed).
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[edit]

SBX underway

Important applications include:

 Servicing Aids to Navigation (ATON)

 Cable-laying
 Crane vessels
 Cruise ships
 Diving support vessels
 Dredging
 Drillships
 Floating production storage and offloading units (FPSOs)
 Flotels
 Landing platform docks
 Maritime research
 Mine sweepers
 Pipe-laying ship
 Platform supply vessels
 Rock dumping
 Sea Launch
 Sea-based X-band radar
 Shuttle tankers
 Survey ships

Scope[edit]
A ship can be considered to have six degrees of freedom in its motion, i.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.e., the three axes: surge, sway and yaw.

Requirements[edit]
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.
 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.
Maintaining a fixed position is particularly difficult in polar conditions because ice forces
can change rapidly. Ship-borne ice detection and mitigation is not sufficiently developed
to predict these forces, but may be preferable to sensors placed by helicopter.[3]

Reference systems[edit]
Position reference systems[edit]
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 systems have been developed during the past decades.
Producers of DP systems are: Marine Technologies LLC, Kongsberg Maritime, Navis
Engineering Oy, GE, DCNS, Wartsila (ex L-3), MT-div.Chouest,[check spelling] Rolls-Royce
plc, Praxis Automation Technology. The applications and 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. 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.[4] There are also systems
installed on vessels that use various Augmentation systems, as well as combining
GPS position with GLONASS.[5]
 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 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:
o 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.
o 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.
o 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.[6]
 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.

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 from Guidance Marine led to the
development of the SceneScan sensor which is a target-less laser PRS leveraging
on the SLAM algorithm.[7]
 Artemis. A radar-based system. A unit is placed on a FPSO (Fixed Station) and the
unit on board the Shuttle Tanker (Mobile Station) locks to report the Range and
Bearing. The 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.[8]
 DARPS, Differential, Absolute and Relative Positioning System. Commonly used
on shuttle tankers while loading from a 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[9] and RadaScan. These are radar based system, while the RADius have 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.[clarification needed] This enhanced the DPO's
situational awareness. These systems usually have responders which are active
targets that sends the signal back to the sensor to report the range and bearing. The
range is typically up to 600 meters.[citation needed]
 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 reference systems[edit]
 Gyrocompasses are normally used to determine heading.
More advanced methods are:

 Ring-Laser gyroscopes
 Fibre optic gyroscopes
 Seapath, a combination of GPS and inertial sensors.
Sensors[edit]
Besides position and heading, other variables are fed into the DP system
through sensors:

 Motion reference units, vertical reference units or vertical reference sensors ,

VRUs or MRUs or VRSs, determine the ship's roll, pitch and heave.
 Wind sensors are fed into the DP system feedforward, so the system can anticipate
wind gusts before the ship is blown off position.
 Draught sensors, since a change of draught influences the effect of wind
and 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[edit]
Block diagram of control system

In the beginning PID controllers 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 hydrodynamic and aerodynamic description concerning some of the ship's
characteristics such as mass and 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
filtering 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[edit]

North Sea Giant

To maintain position azimuth thrusters (electric, L-drive or Z-drive) bow thrusters, stern
thrusters, water jets, rudders and propellers are used. 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. These fluctuations may
be suitable for hybrid operation. An LNG-powered platform supply vessel started
operation in 2016 with a 653 kWh/1600 kW battery acting as spinning reserve during
DP2, saving 15-30% fuel.[10] The 154-meter North Sea Giant has combined 3
powerpacks, switchboards and 2 MWh batteries to operate in DP3 using only one
engine,[11][12] keeping the engine load between 60-80%.[13]
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.

Class requirements[edit]
Based on IMO (International Maritime Organization) publication 645[14] the Classification
Societies have issued rules for Dynamic Positioned Ships described as Class 1, Class 2
and Class 3.

 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:

BV NK ABS GL DNV LR IMO Description

Equipme Equipme Equipme Equipme Equipme Equipme Equipme
nt Class nt Class nt Class nt Class nt Class nt Class nt Class

Manual
position
control and
automatic
heading
DYNPO control
- DPS-0 - DP(CM) -
S-AUTS under
specified
maximum
environme
ntal
conditions

DYNAP DPS A DPS-1 DP 1 DYNPO DP(AM) Class 1 Automatic

OS S-AUT & and
AM/AT DPS1 manual
position
and
heading
control
 under
specified
maximum
environme
ntal
conditions

DYNAP DPS B DPS-2 DP 2 DYNPO DP(AA) Class 2 Automatic

OS S-AUTR and
AM/AT R & DPS2 manual
position
and
heading
control
under
specified
maximum
environme
ntal
conditions,
during and
following
any single
fault
excluding
loss of a
compartme
nt. (Two
independe
nt
computer
systems).

DYNAP DPS C DPS-3 DP 3 DYNPO DP(AAA Class 3 Automatic

OS S- ) and
AM/AT AUTRO manual
RS & DPS3 position
and
heading
control
under
specified
maximum
environme
ntal
conditions,
during and
following
any single
fault
including
loss of a
compartme
 nt due to
fire or
flood. (At
least two
independe
nt
computer
systems
with a
separate
backup
system
separated
by A60
class
division).

DNV rules 2011 Pt6 Ch7 introduced "DPS" series of classification to compete with ABS
"DPS" series.

NMA[edit]
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[edit]
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.[15]

This section needs

expansion. You can help
by adding to it. (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.[15]

 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. [16]
 Mitigation – dealing with a runoff – training and competence – emergency drills. [15]
Dynamic positioning alarm and runout response for bell
divers[edit]
 Code amber /Yellow alert - Divers return to the bell immediately, stow umbilicals, and
stand by for further developments and instructions.[17]
 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.[17]
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.[18]

Redundancy[edit]
Redundancy is the ability to withstand, while on DP mode, the loss of equipment which is
online, without losing position and/or heading. 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 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
(FMEA) study and proved by FMEA trials.[19] Besides that, annual trials are done and
normally DP function tests are completed prior to each project.

DP operator[edit]
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[20] as acceptable standard.
To qualify as a DP operator the following path should be followed:

1. a DP Induction course + On-line Examination

2. a minimum of 60 days seagoing DP familiarisation
3. a DP Advanced course + On-line Examination
4. a minimum of 60 days 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 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.

IMCA[edit]
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.[21] It represents offshore, marine and underwater
engineering contractors. Acergy, Allseas, Heerema Marine Contractors, Helix Energy
Solutions Group, J. Ray McDermott, 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,[22] 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[edit]
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.

IMO DP
CLASSIFICATION
OVERVIEW OF IMO DYNAMIC
POSITIONING - DP CLASS
REQUIREMENTS
Based on IMO - International Maritime Organization
publication 645 the Classification Societies have issued rules
for dynamically positioned ships described as Class 1, Class
2 and Class 3.

Dynamic positioning system -

illustrating auto position mode
  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 SYSTEM OVERVIEW

The following table gives an overview of the IMO dynamic
positioning system classification system and the roughly
corresponding dynamic positioning system class notations,
individual variations exists.

LRS ABS IMO

DNV DP DP DP DP
Class Class Class Class Description

DPS 0 Manual position control and auto

DYNPOS- DP DPS- heading control under specified
AUTS (CM) 0 - maximum environmental conditio

DPS 1 Automatic and manual position a

DYNPOS- DP DPS- Class heading control under specified
AUT (AM) 1 1 maximum environmental conditio

Automatic and manual position a

heading control under specified
maximum environmental conditio
DPS 2 during and following any single fa
DYNPOS- DP DPS- Class excluding loss of a compartment
AUTR (AA) 2 2 independent computer systems).
 LRS ABS IMO
DNV DP DP DP DP
Class Class Class Class Description

Automatic and manual position a

heading control under specified
maximum environmental conditio
during and following any single fa
including loss of a compartment
fire or flood. (At least two indepe
DPS 3 computer systems with a separat
DYNPOS- DP DPS- Class back-up system separated by A6
AUTRO (AAA) 3 3 class division).

AVAILABLE DYNAMIC
POSITIONING SYSTEMS
 Go to Dynamic Positioning system overview

RELATED


DYNAMIC POSITIONING SYSTEM MODES

AND FUNCTIONS
Our dynamic positioning systems can be operated in a
variety of different modes.


DYNAMIC POSITIONING BASIC PRINCIPLES

A seagoing vessel is subjected to forces from wind, waves
and current as well as from forces generated by the
propulsion system. The Dynamic positioning - DP
automatically maintain the…

DYNAMIC POSITIONING SYSTEM

REDUNDANCY PRINCIPLE
A dynamic positioning system is a system that automatically
controls a vessel’s position and heading exclusively by use
of active thrust.