Real Life Incident: Human Error Causes Loss Of Power On DP Vessel

Crew on a DP vessel were performing maintenance on the main power distribution bus circuit breakers; maintenance which was several years overdue. Additionally, the maintenance was conducted during a critical Outer Continental Shelf activity. In support of the circuit breaker maintenance, the vessel was transitioning from a ‘closed bus’ operation to an ‘open bus’ configuration with 50% of the vessel’s thrusters operating on each bus.

After opening the bus tie, a generator protection circuit failed to function properly, and this combined with a design flaw in a power transformer protection circuit causing half of the vessel’s thrusters
to stop. The vessel’s engineer attempted to restore power to these thrusters by closing the bus tie without synchronising two live buses (crash sync). Design features and operational procedures to prevent such an action and consequences were not sufficiently in place. The design deficiency allowed a power transient to cause a total loss of thrust and therefore loss of position.

Image for representation purpose only

Lessons learned

  1. The vessel did not have a defined Critical Activity Mode of Operation (CAMO). Ensure a vessel has a defined CAMO and is operating in its CAMO during critical OCS activities.
  2. Ensure the DP operations manual and SMS both appropriately address DP equipment inspection, repair and maintenance requirements. A vessel should not perform maintenance that may cause a loss of position during a critical OCS activity.
  3. An equipment failure, an operational error and multiple failure modes not identified in the vessel’s Failure Modes and Effects Analysis (FMEA) combined to produce the loss of position.
  4. Ensure a structured competence assurance programme is applied to all key DP personnel. At a minimum, DP personnel should be required to demonstrate proficiency in understanding the redundancy concept and emergency procedures in intervening for failed redundancy. Intervention proficiency in restoring power and thrust should be demonstrated during drills and annual trials.

Reference: nautinst

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  1. Familiar with the dp unit. Been in the industry 20 years just about have experienced all the dp units here in the gulf. The one mentioned is not without fault.

  2. Vessel PMS failure pointed to the electric power system basicly. And lack of experience with DP system make it failure.

  3. 1. Why was maintenance on circuit breakers due for several years?
    2. Why cannot the company provide shore support ?
    3. Why didn’t ship superintendent object to lack of maintenance?

    It is wrong to blame seafarer for every accident/incident as its easy way out for office management team. Engineers are not given sufficient downtime in order to carry out maintenance. Moreover such jobs are not taken up in dry dock period in order to get the ship out fast of dock.

    So why blame engineers?

  4. Biggest mistake here is trying to do maintenance during a critical operation, normal standard is to do this in between locations, but it looks like because of some maintenace beeing way overdue they pused the envelope (I know this will happen because the company ashore sees the figures of overdue items every end of the month and will keep pushing you to resolve them even if operations don’t allow it, one thing I don’t understand how it could be overdue for several years means management ashore was not realy helpfull), been there and done it.
    30 years on DP vessels of which 18 years as Chief Engineer.

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