Efficient DP Operation
Some vessels operate with dynamic positioning, DP, meaning the vessels remain stable at the same position independent of external effects such as wind, waves and currents. DP operations form an integral part of offshore vessel operations, however, with different emphasis for the different stakeholders. IMO, Flag States, Classification Societies and Charterers set stringent requirements regarding e.g. equipment capabilities, redundancy, system testing and training of officers. However, there is little focus on efficient utilization of equipment. By focusing and implementing tasks for efficient DP operation, fuel savings can be gained.
Efficient DP operation is to improve the operation of when a vessel is in DP mode, or reduce the time operating in DP. Improving DP operation should be undertaken through identifying and establishing a common approach/understanding regarding DP operation within the company, recognizing variations in operations between the different segments. This should emphasize the importance of standardizing DP operation throughout the fleet. It should also clearly state expectations to the fleet in terms of future DP operation including clear instructions to the vessels on how to implement on board.
Applicability and assumptions
Efficient DP operation is applicable for all ages of vessels with a DP system. DP systems vary greatly depending upon a number of differentiation factors, for example the age of a vessel, leading to different functionalities and capabilities of equipment. Additionally, equipment varies between different manufacturers. However, the main functionalities of the equipment should be standardized for all. Due to the complexity of the systems and also to the importance of position keeping capabilities, the specifications and functionality of DP systems are tightly controlled.
With regards to fuel efficiency, it is critical that operations are optimized to a large extent as possible as offshore vessels spend a large percentage of time operating in DP mode.
For efficient DP operation, it is beneficial to develop a company policy and guidelines regarding Energy Efficient DP operation. The guidelines should emphasize the importance of standardizing DP operation throughout the fleet. It should also clearly state expectations to the fleet in terms of future DP operation including clear instructions to the vessels on how to implement. A guideline may include, depending on type of operation, modes, configuration and installed DP system, the following:
- Utilize Activity Operational Planning to establish the Safest Mode of Operation, Task Appropriate Mode and Activity Specific Operating Guidance, and subsequently a framework for when to utilize each in order to maximize energy efficiency within DP operations.
- Open/Closed Bus operations: Depending on equipment class, see IMO MSC/Circ.645, the open/closed bus operations should be evaluated whether the operation may be conducted in a more efficient manner (i.e. shutting down elements of the system if not required).
- Implement drifting as alternative to DP operation if appropriate: This could be implemented primarily on board OCV vessels.
- Implement anchoring as alternative to DP operation: It is recognized that this recommendation is limited to areas where depth of water facilitates.
- Optimizing gain settings: Standardizing and placing focus on utilization of gain settings can realize energy savings with a minimum corresponding loss of position integrity.
- Use of relaxed DP modes: Only relevant for those vessels with the functionality existing in the equipment on board. Green DP may be utilized as a more energy efficient mode of operation in operations where a lesser degree of position accuracy is required, but the vessel is still required to operate in the DP mode.
- Utilizing manual control in clearly defined scenarios: In certain scenarios the use of manual control may assist with a reduction in consumption compared with operating in DP mode. For example, using the main propulsion to maintain position rather than operating in DP (vessel steams slowly into the wind making way and maintaining heading through use of the engine rather than thrusters).
Cost of implementation
There are no direct costs related to efficient DP operation. However, there might be costs related to training of crew to improve the performance, production of guidelines or software tools to track the performance of this as a measure.
The assumed reduction potential is 1% of total ship fuel consumption. However, it is important to highlight that the reduction potential in DP is 2% to 5 % of the fuel consumed in DP, as the time in DP varies significantly for different vessels.
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