Question 1

You've just taken over a DP watch. Ten minutes into your watch, checking the DP logbook properly, you find a note from two hours ago that DGNSS Unit 2 was showing intermittent dropouts. Looking at the DP reference panel now, you can see Unit 2 is indeed showing reduced position confidence — a fact the outgoing DPO did not mention.

What do you do?

Accepted Answer

Immediately inform the master that a reference degradation that predates your watch was not communicated at handover, formally reassess the current ASOG status, and consider whether a retrospective consequence analysis is needed given the current reference configuration. This is also a handover quality failure that needs to be raised through the SMS A reference system degradation that was not passed on at handover means you have been operating for 10 minutes without full situational awareness of the system state you accepted. The master needs to know immediately — both because of the current degraded configuration and because a handover failure has occurred that needs SMS review. Waiting to see if it recovers delays informing the master of a risk that already exists. Calling the outgoing DPO first before escalating to the master is also the wrong priority — the safety issue comes first, the handover quality issue is secondary. IMCA M117 requires a systematic handover; when that fails, the discovery must be escalated immediately.

Question 2

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 3

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.