Dynamic Positioning Systems
This page gives an overview of Dynamic Positioning (DP) systems. Please see the DP Policy & Guidance and DP Voluntary Reporting tabs for additional regulatory information.
For additional, detailed information and references, please see the Introduction to Dynamic Positioning (DP) Systems guide.
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Uses of DP Systems on the OCS
A Dynamic Positioning System is a computer-controlled system used to automatically maintain a vessel’s heading and position without the use of mooring lines and/or anchors.
Since it was first introduced in the 1960s, DP Systems have evolved to become the primary means of station keeping for vessels operating on the U.S. Outer Continental Shelf (OCS). DP Systems are often used on Mobile Offshore Drilling Units (MODUs), Floating Production Units (FPUs), Construction Vessels, Accommodation Vessels (Floatels), Dive Support Vessels, Offshore Supply Vessels (OSVs), cable and pipe-laying vessels and shuttle tankers.
The DP system is used to maintain the vessel’s position in order to conduct critical activities such as drilling, diving operations, under water construction, and close quarter activities such as bulk cargo transfers, fuel transfers, deck cargo operations, personnel transfers, and ROV work.
A DP System is comprised of three sub-systems:
These three sub-systems work in unison to maintain the vessel’s heading and position by controlling the horizontal movement of the vessel.
The power system is comprised of all components and associated systems necessary to supply the DP system with power.
The power system includes but is not limited to:
The power supply should be reliable and adequate to provide continuous power to the DP control system, thrusters/propulsion systems and all of the vessel’s other operational loads or power demands so that the DP system can maintain the vessel’s desired position and heading.
The thruster system is comprised of all components and associated systems necessary to supply the DP system with variable force and direction of thrust.
The thruster system includes:
The thruster system shall be arranged as to provide the vessel with adequate maneuverability under all operating conditions. Also, the thruster system should be able to provide adequate thrust to control surge, sway and yawing.
Thruster systems should be arranged so that the failure of any part of the system including pitch, azimuth or speed control should not increase the thrust magnitude or direction.
Individual thruster emergency stop systems should be arranged in the DP control station.
DP Control System
The DP control system is comprised of all control components and associated systems, hardware and software necessary to coordinate with the other sub-systems to maintain position.
The DP control system includes:
The control computers receive input from various sensors and reference systems to determine the vessel’s heading, position and the external forces being applied to the vessel. This information is then processed to determine the amount and direction of force that must be applied in order to counteract the external forces. The Power and Thrusts sub-system then execute the commands given from the control system and exerts the desired force needed to maintain the desired heading and position.
Classes of DP Systems
The IMO has categorized DP Systems into three equipment classes based on redundancy and protection. The necessary redundancy level for the components and systems are determined by the consequence of the loss of vessel position and/or heading.
The classes are stated below as defined in IMO MSC.1/Circ. 1580:
A loss of position and/or heading may occur in the event of a single fault.
Position Reference Systems
In order for the DP System to keep a vessel in a desired position, it must utilize a Position Reference System (PRS). The PRS identifies the vessel’s current position. This position will either be an absolute position (geographic position) or a relative position (relative to a target).
There are several systems, which utilize either absolute or relative positions. Some of these systems and some common brand names are:
Relative: Laser (Cyscan®, Fanbeam®), Microwave (Radascan®), and Tautwire
Absolute: Satellite (DGPS, DGNSS), and Underwater Acoustics (HPR)
When two or more position reference systems are used or required, they should not be of the same type, and should be based on different principles and suitable for the operating conditions.
Environmental & Motion Sensors
Vessel should be equipped with sensors to measure heading, vessel motion and the wind speed and direction.
These sensors include:
Gyro: The gyrocompass constantly provides the DP computer with the vessel’s current heading data in order to maintain and/or control vessel’s heading.
Wind: Input from wind sensors are needed for the controller to measure the effects of the wind on the sail area of the vessel.
Motion Sensors: These sensors measure 3 of the 6 degree of motions that are not controlled, but must be accounted for to improve accuracy of the position reference systems.
Sensors for the same purpose which are connected to redundant systems should be arranged independently so that failure of one will not affect the others. Example: the three gyrocompasses that are providing input data into the two DP computers should be arranged that failure of one gyrocompass shall not affect the remaining two gyros.
Human Element (DP Operator)
The DP operator should be:
The required training, familiarization and/or certification of the DP personnel on board will be included in the approved DP Operations Manual.
DP Operations Manual
A DP Operations Manual is required as part of the plan review and approval. The DP Operations Manual should be vessel specific and located near the DP Operator’s Station, readily available to the DPO for quick reference during DP Operations. DP operations should be conducted in accordance with the approved DP Operations Manual.
DP Operations may be considered “Key Shipboard Operations” as stated in Regulation 7 of International Safety Management (ISM) Code. Therefore, the DP Operations Manual may also be part of the vessel’s Safety Management System (SMS).
The requirement for the vessel specific DP Operations Manual is in addition to the manufacturer’s Owner’s or Operator’s Manual.
The requirements for the contents of the DP Operations Manual differ depending on the approving authority. However, most DP Operations Manual will normally include the items listed below:
DP System Plan Review and Approval
For U.S. Flagged vessels, the DP System’s Plans and Documents should be approved by the U.S. Coast Guard’s Marine Safety Center (MSC) or an ACS/RO on behalf of the Coast Guard. Evidence of approval will be a copy of stamped Plans/Documents, and Reviewed/Approved Letter from the approving authority. There should also be records of the completed Proving Trials on board that should be stamped reviewed/approved.
DP Documents that should be reviewed and approved are:
The Marine Safety Center oversees plan review and other technical work performed by ACS/ROs for U.S. Flagged vessels and has published several guidance documents regarding the review and approval of plans for DP systems. Two of them that are commonly known and used are; MSC’s MTN 02-11, CH-1 and PRG E2-24.
Marine Safety Center MTN 02-11, CH-1
The Marine Safety Center has published a Technical Note for DP Plan Submittal and Approval (MSC’s MTN 02-11, CH-1) which provides guidance for submitting plans to the MSC, or to an Authorized Classification Society (ACS) conducting review of these systems on behalf of the Coast Guard. Enclosure (2) of the MTN allows the submitters to submit plans using the IMO MSC/Circular 645 Guidelines for vessels with DP Systems as the baseline for the design, or cite the relevant Classification Society Rules for the design.
Marine Safety Center PRG E2-24
In addition to MTN 02-11, the Plan Review Guideline (PRG) titled “E2-24 Dynamic Positioning Systems” will assist the plan submitters with preparing and submitting a DP system plan to the Marine Safety Center.
Surveys, Tests & DP Verification Acceptance Document
DP Failure Modes and Effects Analysis (FMEA)
A FMEA is a systematic analysis of systems and sub-systems to a level of detail that identifies all potential failure modes down to the appropriate sub-system level and their consequences.
DP Proving Trials
A survey and proving trials should be conducted to confirm the expected effects of the failure modes found in the FMEA desktop analysis.
DP Periodic Trials
A survey and periodic trials should be completed every 5 years using similar test procedures as the DP Proving Trials.
DP Annual Trials
The annual survey and tests of the DP system and components should be completed within 3 months before or after the anniversary date of the DPVAD or initial survey.
Either a general or partial survey and test, depending on the circumstances, should be carried out each time a defect is discovered and corrected or after an accident occurs which affects the safety of the DP vessel, or whenever any significant repairs or alterations are made.
DP Verification Acceptance Document (DPVAD)
This document should be issued by the Flag State or RO to vessels that comply with the IMO DP guidance (IMO Circ.645 or Circ.1580), as applicable.
Note: Because the U.S. Coast Guard does not have any regulations regarding DP systems, DPVADs are not normally found on U.S. Flagged vessels. Verification of DP systems would be found on the appropriate Classification Certificate.