US Coast Guard on Dynamic Positioning Systems: Don't overestimate their capabilities!
Nov 07, 2022
1 min read
The United States Coast Guard has published the safety alert entitled "Dynamic Positioning Systems: Don't overestimate their capabilities!". This document has been issued on November 1st, 2022.
The US Coast Guard has published this document because recently investigated Dynamic Positioning (DP) incident revealed that a DP system may still have weaknesses, even when the design and testing of the system aims to remove or mitigate those weaknesses through engineering controls.
During the recent incident, a DP3 drillship suffered a complete blackout and subsequent loss of position while conducting critical Outer Continental Shelf (OCS) activities.
The drillship was equipped with highly-complex power management, generator monitoring, control, and safety systems designed and tested to provide blackout protection and rapid blackout recovery.
This particular ship had equipment arrangements that exceeded minimum DP equipment class 3 requirements and was approved for, and operating with, the 11kV electrical system connected in a “closed-bus” configuration.
The drillship was performing critical well activities where a loss of position could result in personal injury, environmental pollution, or catastrophic damage.
Fortunately, these serious consequences were avoided due to the successful post-blackout actions taken by the crew, which included performing an emergency disconnect from the well using established procedures.
The investigation determined that a defective vacuum interrupter (VI) caused a cascading electrical failure that ultimately caused the blackout.
A Dynamic Positioning system (DP system) is defined by IMO MSC.1/Circ.1580 as the complete installation necessary for dynamically positioning a vessel comprising, but not limited to, the power system, the thruster system and the DP control system.