For Equipment Class 3 vessels, at least one position reference sensor should be directly connected to which system?

For Equipment Class 3 vessels, the requirement is that at least one position reference sensor must be directly connected to a backup control system that is independent of the position reference systems. This is crucial for ensuring redundancy and reliability in the vessel's dynamic positioning (DP) operations.

In the context of DP systems, a backup control system that is separate from the primary position reference systems allows for continued operation even if the primary sensors fail or provide inaccurate data. This independence is vital for maintaining the safety and operational integrity of the vessel, particularly in critical situations where precise positioning is essential.

In contrast, the other systems mentioned, such as the main engine control system, primary power system, and ballast control system, do not offer the same level of redundancy for position reference. Connecting the position reference sensor to these systems does not provide the necessary independence or reliability required for Equipment Class 3 operations, which is why these alternatives do not meet the necessary requirements for the vessel's DP capabilities.