Question 1

A DP2 vessel is holding position near a platform with three position reference systems online: DGNSS 1, DGNSS 2, and a Fanbeam. DGNSS 1 suddenly drops out completely with no warning. What is the DPO's immediate first action?

Accepted Answer

Confirm the DP system has automatically excluded DGNSS 1 from the position solution and is now running on the two remaining references (DGNSS 2 and Fanbeam); verify the resulting position solution is stable before doing anything else With two valid references still online and voting correctly, the DP system should auto-exclude the failed sensor and continue safely. The DPO's job is to confirm this happened correctly and that the remaining solution is sound — not to panic-switch to manual, nor to assume everything is automatically fine without checking.

Question 2

With DGNSS 1 excluded, the vessel now relies on DGNSS 2 and Fanbeam only. What should the DPO do differently now compared to when three references were available?

Accepted Answer

Increase monitoring vigilance specifically — with only two references, there is no longer a "voting" majority if one of the remaining two starts to disagree, so any divergence between DGNSS 2 and Fanbeam now requires immediate judgement rather than automatic resolution; the DPO should also consider what reference would be left if either of these also fails Voting logic depends on having enough independent references to identify which one is wrong when they disagree. With three, a 2-vs-1 split is usually resolvable; with two, any disagreement is ambiguous — the DPO cannot automatically tell which reference, if either, is correct. This loss of voting power is the real operational change, not just "one fewer sensor".

Question 3

Twelve minutes later, the Fanbeam laser loses lock on its target due to a passing rain squall reducing visibility. The vessel is now running on DGNSS 2 alone. What is the immediate implication?

Accepted Answer

The vessel now has a single, unverified position reference with no independent cross-check — this is a significant escalation requiring an immediate ASOG review and likely a move toward the amber/red alert posture, since any undetected fault in DGNSS 2 would now go unnoticed by the DP system A single reference with no cross-check is the position-keeping equivalent of flying blind to any subtle fault in that one system — there is nothing left to detect a slow drift or bias. This is exactly the point at which ASOG should be escalating the alert posture, regardless of how "stable" the single reference currently looks.

DP — Reference System Loss (Cascade) Practice Questions