Efficient DP Operation

Some vessels operate with dynamic positioning, DP, meaning the vessels maintain its position with only minimal effect of external loads such as wind, waves and currents. DP operations form an integral part of offshore vessel operations, however with different emphasis for the different segments. IMO, Flag States, Classification Societies and Charterers set stringent requirements regarding e.g. equipment capabilities, redundancy, system testing, and training of officers. In recent years there has also been an increasing focus on energy efficiency in DP operation. By focusing and implementing task for efficient DP operation fuel savings can be gained.

Efficient DP operation is either to improve the actual operation 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 towards 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 onboard.

Applicability and assumptions

Efficient DP operation is applicable for all ages of vessels with a DP system typically offshore vessels and shuttle tankers. 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. Also, equipment varies between different manufacturers, however the main functionalities of the equipment should be standardised 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 optimised 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. he guidelines should emphasise the importance of standardising 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 onboard. A guideline may include, depending on type of operation, modes, configuration and installed DP system the following:

• Utilise 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 utilise each in order to maximise 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 onboard OSV vessels (discussion & agreement should take place at relevant level within the charterer as there is a risk that the client onboard would not accept/like the recommendation). There is also a potential for PSV and AHTS vessels to implement drifting. It is recommended that this be included as part of the ASOG analysis above.
• Implement anchoring as alternative to DP operation: It is recognized that this recommendation is limited to areas where water depth allows for this.
• Optimising gain settings: Standardising and placing focus on utilisation of gain settings can realise energy savings with a minimum corresponding loss of position integrity.
• Use of Relaxed/green DP modes: Only relevant for those vessels with the functionality existing in the equipment onboard. Green DP may be utilised 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.
• Utilising 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 automatic DP mode. For example, using the main propulsion to maintain position rather than operating in DP (steam slowly into the wind so that the vessel is making way, slowly 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.

Reduction potential

The assumed reduction potential is 1% of total ship fuel consumption. However, as the time in DP varies a lot for different vessels, the reduction potential in DP mode would be about 2 – 5 %.

Other References

1. IMO MSC/Circ. 645 / Guidelines for vessels with dynamic positioning systems
2. Kongsberg K-POS / Dynamic positioning. Optimizing complex vessel operations
3. Dinh, H.T., et al., 2018. Optimal Energy Management for Hybrid Electric Dynamic Positioning Vessels