An operator of a floating platform or inputs time periods when he claims to have operated a vessel in dynamic positioning mode 201. Data representing the state of the vessel 202 e.g. speed, position, heading, and parameters affecting the position of the vessel 206 e.g. weather and ocean data, over those periods of time is received. The data is processed to remove times when an operational state of the vessel comprises a prohibited state 203-205 and the modified data is used to determine a trajectory of the vessel in relation to the parameters affecting the position of the vessel 215. The trajectory is compared with a threshold e.g. comprising position and speed parameters, to determine whether the vessel was actually being operated as the operator claimed 216-217. The prohibited state may include when the vessel moves with the wind direction or tide, indicating it is allowed to drift or operates above a predefined speed indicating the vessel is in transit. Data may also include position, proximity and orienta
