4.1. DP Capability Plots

DP capability defines a DP vessel's station-keeping ability under given environmental and operational conditions. DP capability analyses are used to establish the maximum weather conditions in which a DP vessel can maintain its position and heading for a proposed thruster configuratioin.

To prepare a DP capability curve for a certain vessel wind, current and waves are normally taken to act in the same direction. Environmental forces and moments are increased until they are exactly balance by the maximum available thrust offered by the thruster configuration. By letting the environmental components rotate in steps around the vessel the results of a DP capability analysis can be presented by means of a limiting mean wind speed for a discrete number of wind angles of attack. 

4.2. DP capability plot - Explained

Below is  DP capability plot for a semi-submersible. The blue line shows the maximum wind speed at which the DP system can maintain position and heading. For each direction the maxiumum wind speed is differend because of the exposed length and shape of the vessel is not the same. However the plot is usually symmetric since vessels are typically symmetric.

Dynamic Positioning - Capability Plot

DP capability plot assumptions

Allowance: Spare thrust to compensate for the hydrodynamic behavior of wind and wave drift loads (capability plots for static loading). Thrust force are taken into account (reduction due to current, hull-thruster interaction etc)

DP Feasibility plot
A DP Feasibility plot shows if the vessel can operate in a given environment and determines the power consumption.