Question 1

You're on DP2 watch during a cable survey operation. The ROV pilot requests you shut down the port aft azimuth thruster because its cavitation noise is interfering with the multibeam sonar. The thruster is currently not contributing significant thrust in the prevailing conditions. You shut it down.

What critical DP risk has this action introduced?

Accepted Answer

Shutting down a thruster changes the Worst Case Failure and may remove the vessel from DP2 compliance — the remaining thruster configuration must now be consequence-tested to confirm DP2 capability is maintained, and the ASOG status must be reassessed before operations continue Even a thruster contributing little current thrust is part of the vessel's redundancy configuration. Shutting it down may change which thruster now becomes the WCF, and the consequence analysis result for the new configuration has not been verified. IMCA 2024 incident data specifically recorded cases where DPOs deactivated thrusters in response to operational requests (noise, vibration, ROV interference) without reassessing the WCF impact — with some subsequently operating outside DP2 class capability without knowing it. The ROV team's operational preference cannot override the DP2 redundancy requirement without a formal reassessment and ASOG review.

Question 2

During a DP2 anchored-spread mooring operation, your two DGNSS systems begin showing positions that diverge by 4.2 metres and are moving further apart. The Fanbeam is not available at this worksite. Both DGNSS units show normal signal strength and differential correction status.

What is your immediate decision process?

Accepted Answer

With two diverging DGNSS units and no third reference, you cannot determine which is correct. Immediately inform the master, assess whether operations can safely continue with degraded reference confidence, and consider whether an additional reference source (taut wire, radar range/bearing, another DGNSS unit) can be deployed or activated before the divergence worsens Two reference systems that disagree cannot be arbitrated without a third — you simply cannot know which is correct. Averaging two potentially erroneous positions may drive the vessel toward the error. This situation directly mirrors the gyrocompass argument for having three units: with only two, a disagreement produces a binary uncertainty with no way to resolve it. The correct response is to treat this as a reference degradation event, inform the master, and seek a third independent reference before the situation develops. Operating near a mooring spread with an unresolved 4.2m reference discrepancy that is growing is a significant risk.

Question 3

You're DPO on a DP3 semi-sub on station over a well. Wind has reached 38 knots — two knots above your ASOG red abort limit. The toolpusher calls the bridge: 'I need 20 more minutes or we'll have to re-drill this section from scratch. It\'s worth millions. Just hold it.'

You have authority to initiate the emergency disconnect. What do you do?

Accepted Answer

Initiate the emergency disconnect sequence immediately per the ASOG, inform the master, and advise the toolpusher clearly that the ASOG abort criteria have been met — the disconnect cannot wait for commercial resolution. The financial decision about re-drilling is the client's problem, not a reason to operate outside the agreed safety envelope IMCA DPE 03-24 ("There — but not really there") specifically examined cases where DPOs remained on station beyond ASOG limits under commercial pressure. The ASOG red criteria are pre-agreed abort triggers set when commercial pressure was not the immediate factor — they exist precisely to provide a clear line that cannot be re-negotiated in real time. The DPO's authority to abort is not conditional on the toolpusher's agreement or the master's approval when red criteria are met. The millions at stake in re-drilling are also at stake if a riser fails under uncontrolled conditions — and so is the well.

DP — What-If (DPO) Practice Questions