Katerina Swanson
Dynamic positioning (DP) is a computer-controlled system that automatically maintains a vessel's position and heading using its own propellers and thrusters. It is primarily used to control the ship in the horizontal plane, i.e., the translation along the two horizontal axes (surge and sway) and rotation on the vertical axis (yaw). The DP system calculates the required thrust to maintain the position of the vessel by measuring its position, the forces acting on it, and its movements. While DP systems offer several advantages, such as enabling various operations and improving safety, they also come with limitations, including high fuel consumption and increased maintenance costs. This text aims to explore the topic of dynamic positioning systems and analyse how much extra fuel they utilise.
| Characteristics | Values |
|---|---|
| Fuel Consumption | High |
| Maintenance Cost | High |
| OPEX | High |
| Positioning System | GPS |
| Power System | Prime movers with necessary auxiliary systems |
| Power System Components | Fuel, cooling, pre-lubrication and lubrication, hydraulic, pre-heating, and pneumatic systems |
| DP Class 1 System | No power redundancy required |
| DP Class 2 System | Power redundancy provided |
| DP Class 3 System | Bus-tie breaker must be open during DP operation |
| DP Controller | Computer/controller/process station |
| DP Operator | Deck watchkeeping officer |
| DP Operator Qualification Renewal | Every 5 years |
| DP Function | Control of the ship in the horizontal plane |
| DP Components | Position reference systems, thrust elements |
| DP Vessel Movement | Surge, sway, and yaw |
| DP Use Case | Maintaining a fixed position, sailing an exact track |
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What You'll Learn
Fuel consumption and DP systems
Dynamic positioning (DP) systems are now commonly used to keep vessels stable and in a fixed position, replacing the traditional method of anchoring. They are particularly useful for offshore drilling vessels, support vessels, and pipe-laying and offshore construction vessels. DP systems use thrusters and propellers to balance environmental forces, such as wind, waves, and currents, which would otherwise move the vessel off its desired position.
DP systems are computer-controlled and use sensors to monitor the position of the vessel, as well as the magnitude and direction of environmental forces. This information is fed into a computer program, which contains a mathematical model of the vessel, including wind and current drag and thruster location. The computer then calculates the required steering angle and thruster output to maintain the vessel's position.
The DP system can be divided into seven components, including position reference sensors, motion sensors, wind sensors, and a gyrocompass, which all provide information to the computer. The DP computer/controller/process station then takes inputs from these sensors and gives orders to the thrusters, which is known as thrust allocation logic (TAL). The operator of the DP system plays a vital role in managing safety and must be able to step in if the system fails.
DP systems have high fuel consumption, and the amount of fuel used will depend on the DP class of the ship. DP class 1 ships have a relatively simple system, while DP class 3 ships have a more complex system with higher power requirements. To reduce fuel consumption, some vessels combine powerpacks, switchboards, and batteries to operate in DP3 using only one engine, keeping the engine load between 60% and 80%.
Additionally, some DP systems use a function called Weathervaning DP, which keeps the vessel at a fixed position while allowing the heading to change to minimize environmental load. This results in minimum power requirements and, therefore, reduced fuel consumption.
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DP system components
Dynamic positioning (DP) systems are used to automatically maintain a vessel's position and heading by using its own propellers and thrusters. The main components of a DP system are the positioning system, the DP computer, and the thrusters.
The positioning system, usually a GPS, monitors the position of the vessel. Position reference sensors, combined with wind sensors, motion sensors, and gyrocompasses, provide information to the computer about the vessel's position and the magnitude and direction of environmental forces affecting its position. This allows the computer to calculate the required steering angle and thruster output for each thruster. The DP computer will calculate the required thrust, which will then be applied by the thrusters to maintain the vessel's position.
The number, size, and location of thrusters are determined based on the initial design of the DP system and the environmental conditions in which the vessel is intended to work. The thrusters automatically balance the environmental forces, such as wind, waves, and currents, to keep the vessel in position.
The power system is another critical component of a DP system. It includes prime movers with necessary auxiliary systems, such as piping, fuel, cooling, lubrication, hydraulics, pre-heating, and pneumatics. The power system may be divided into two buses for redundancy, especially in DP class 2 and class 3 systems, to ensure that a failure in one bus does not affect the other and that there is enough power for position-keeping.
Additionally, DP systems may have an Uninterruptable Power Supply (UPS) to provide backup power to critical components such as the controller, console, sensors, and position reference systems in the event of a blackout.
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DP system functions
Dynamic Positioning (DP) systems are used to maintain a vessel's position and heading by using thrusters to automatically balance environmental forces such as wind, waves, and currents. The main components of a DP system are the positioning system, the DP computer, and the thrusters. The positioning system, typically a GPS, monitors the position of the vessel, while the DP computer calculates the required thrust to maintain the vessel's position. The thrusters then generate the necessary forces to keep the vessel in position. This technology was first developed in the 1960s for scientific research and geological surveys and has since become prevalent in the maritime industry.
DP systems have several functions that enable them to maintain a vessel's position and heading. One key function is the ability to calculate and implement the necessary forces to counter the environmental forces acting on the vessel. The DP computer uses information from position reference sensors, wind sensors, motion sensors, and gyrocompasses to determine the vessel's position and the magnitude and direction of environmental forces. It then calculates the required steering angle and thruster output for each thruster to maintain the desired position and heading.
Another function of DP systems is power management. DP vessels typically experience large changes in power demand due to fluctuations in environmental conditions. To handle these variations, DP ships are often diesel-electric, allowing for a more flexible setup. Power management functions include controlling the load of individual generators, sharing the load equally among generators, and monitoring available power to determine if additional generators are needed. In the event of a blackout, DP systems may have an Uninterruptable Power Supply (UPS) that provides power to critical components for a minimum of 30 minutes.
DP systems also offer the ability to maintain a fixed position while allowing the heading to change, known as weathervaning DP. This function aims to minimise the environmental load on the vessel by adjusting its heading to align with the least resistant direction. Additionally, DP systems can be used in combination with mooring to further enhance the vessel's position maintenance.
The operator of a DP system plays a crucial role in managing safety and intervening in the event of system failure. DP operators require specialised training and qualifications to handle their safety-critical role effectively. They utilise a human-machine interface (HMI) to control the DP system, which includes a display, control station, and joystick for manual control of the thrusters.
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DP system redundancy
Dynamic positioning (DP) is a computer-controlled system that automatically maintains a vessel's position and heading using its own propellers and thrusters. DP systems are typically used by offshore vessels for accurate manoeuvring, maintaining a fixed position, or track keeping.
DP systems have different classes, with varying levels of complexity and redundancy. The DP class of a vessel is determined by its redundancy, or its ability to continue DP operations in the event of a component failure.
DP Class 1 vessels can hold their position but have no specific redundancy or operational reliability requirements. They are relatively simple systems.
DP Class 2 vessels meet the requirements of Class 1 but have improved redundancy and operational reliability. They can maintain their position even if an active component fails, allowing the crew to safely stop any work in progress. DP Class 2 systems have two Uninterruptable Power Supplies (UPS), providing backup power to critical systems in the event of a blackout.
DP Class 3 vessels have the most complex systems, with further improved redundancy and physical separation of redundant systems. In the event of a failure or loss of an entire compartment due to fire or flooding, a DP Class 3 vessel can continue operations without affecting the backup system. DP Class 3 systems have three UPS units and watertight separation between compartments.
While redundancy is crucial for DP systems, it is not a guarantee of operational reliability. The effectiveness of redundancy depends on proper configuration, and DP vessel station-keeping incidents can still occur due to poor configuration of critical systems.
Overall, DP system redundancy plays a vital role in maintaining the position and heading of vessels, providing backup power and system separation to ensure uninterrupted operations even in the face of component failures or adverse events.
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DP system training
Dynamic Positioning (DP) systems are used to control the position and heading of a vessel by using thrusters that are constantly active and automatically balance the environmental forces (wind, waves, and currents). DP systems are typically used by offshore vessels for accurate manoeuvring, maintaining a fixed position, or for track keeping.
DP systems have high fuel consumption and maintenance costs. Fuel consumption is influenced by several factors, such as environmental conditions, vessel characteristics, thruster configuration, and the DP algorithm. Therefore, DP operators need to know how different DP control modes affect fuel consumption and how to optimise it for different scenarios.
To qualify as a DP operator, individuals must follow a specific training and certification scheme operated by The Nautical Institute (NI). This includes watchkeeping on a Class 1 DP ship to obtain a limited certificate, or on a higher-class ship for a full certificate. The NI issues logbooks, accredits training centres, and controls the issuance of certification. The International Dynamic Positioning Operators Association (IDPOA) was also created in 2009 to address the increasing manpower demands for DP operators.
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Frequently asked questions
Dynamic positioning (DP) systems use extra fuel to keep a vessel at a fixed position by automatically balancing environmental forces such as wind, waves, and currents. The amount of extra fuel used depends on various factors, including the DP class of the vessel, the number and size of thrusters, and the power management system.
The amount of extra fuel consumed by a DP system depends on several factors, including:
- DP class: Higher DP classes, such as Class 2 and Class 3, may have more advanced power systems and redundancy features, which can impact fuel consumption.
- Thrusters: The number, size, and location of thrusters can vary depending on the vessel's operational requirements, affecting fuel usage.
- Power management: The efficiency of the power management system can influence fuel consumption. Advanced power management systems can optimize fuel usage by controlling generator loads and managing power capacity.
The DP class of a vessel determines the complexity of the system and the power requirements. For example, DP Class 1 systems are relatively simple and may not require power redundancy, while DP Class 2 and Class 3 systems have more advanced power configurations, which can impact fuel efficiency.
Yes, there are fuel-saving techniques employed in DP systems:
- Weathervaning DP: This technique allows the vessel to change its heading to minimize environmental load, reducing power requirements and fuel consumption.
- Power management strategies: Techniques such as preferential tripping, share load functions, and blackout recovery can optimize power usage and reduce fuel consumption.
- Hybrid operation: Some DP ships use a combination of diesel-electric and battery power, allowing for flexible power management and potential fuel savings.
