DNV DNV-ST-0111 PDF

This standard sets requirements for calculation and documentation of DP station keeping capability at three different levels:

— DP capability level 1:

this level sets requirements to a basic and prescriptive static method for documenting DP capability numbers for ship-shaped-mono-hull vessels. The calculations shall be based on a static balance of environmental forces and the vessel's actuator forces. The calculations shall for benchmarking purposes be based on the same specified environmental data for all vessels as specified in Table 2-3 of this standard. The rigidness of the method ensures that the DP capability numbers calculated according to the method shall be comparable between different vessels. The results are documented by DP capability numbers and capability plots.

Guidance note:

In case assessment based on different environmental data than specified in Table 2-1 is wanted, then a DP capability level 2-site calculation may be performed using the DP capability level 1 prescriptive calculation method, as long as this is applicable to the specified environment. Note that in such a case the results cannot be expressed in terms of DP capability numbers as these only relate to the environment specified in Table 2-1.

— DP capability level 2:

this level sets requirements for a more comprehensive quasi-static method and may be applied to all vessel shapes. This level allows for vessel specific adjustments to the calculations. Any vessel specific data shall be documented and justified. The calculations shall be based on a static balance of environmental forces and the vessel's actuator forces, and shall be based on the same specified environmental data as for level 1. The results are documented by DP capability numbers and capability plots.

— DP capability level 2-site:

same as level 2 and in addition the method allows for the use of site specific environmental data, operation specific vessel load condition, and/or inclusion of external forces. Results will only be fully comparable between vessels in case the same calculation method and environment are used for the vessels to be compared. The results are documented by capability plots.

— DP capability level 3:

this level sets requirements for use of time-domain simulations and may be applied to all vessel shapes. Such simulations may e.g. be used in projects where more information about the vessel dynamic capabilities is wanted. Environmental data specified for level 1 shall be used. The results are documented by DP capability numbers and capability plots.

— DP capability level 3-site:

same as level 3 and in addition the method allows for the use of site specific environmental data, operation specific vessel load condition, and/or inclusion of external forces. Results will only be fully comparable between vessels in case the same calculation method and environment are used for the vessels to be compared. The results are documented by capability plots.

In addition to the calculation methods, this standard sets requirements for how to document the calculations and how the results shall be presented. DP capability level 1, level 2 and level 3 results shall be presented in the form of DP capability numbers assigned as specified in Table 2-1 and capability plots. DP capability level 2-site and level 3-site results shall be presented in the form of capability plots showing the limiting wind envelopes based on the site specific environmental data. Reporting shall be performed according to App.A.

Guidance note:

When calculating and evaluating DP capability assessments it should be understood that models, calculation methods, and environment specifications inherently include some inaccuracies and uncertainties. Level 1 provides generic and prescriptive methods and results. In general, when more project or operational specific information is required in such assessments, this can be achieved by applying Level 2/Level 2-site or level 3/level 3-site methods. App.B provides guidance on usage and specification of DP capability assessments according to this standard.