Question 1

Four hours later, Gyros 2 and 3 have been repaired. All three gyros now agree within 0.2°. The UPS units have been tested and confirmed independent. The chief engineer signs off the repairs. The lead DPO says the vessel is ready to return to the 120m working position.

Before returning to the working position, what must the master and DPO team do that goes beyond just confirming the gyros are working?

Accepted Answer

Complete a full pre-operation setup: run consequence analysis test at a safe standoff, review updated ASOG status with the client, brief the full DPO team on what happened and what the new monitoring requirements are (including UPS independence checks), confirm the rig OIM is satisfied with the vessel returning to 120m, and formally record the incident in the DP logbook and official log before resuming Returning to the 120m working position requires the same standard as the initial approach — a consequence analysis test, ASOG status confirmation, rig OIM agreement, and a properly informed DPO team. In addition, the fact that a CCF path (shared UPS) was discovered means the team needs to understand what changed and what to monitor. Running the debrief after returning to position reverses the priority: the debrief ensures the team understand the incident before they return to the risk zone, not after. The principle is: understand what went wrong before returning to the conditions where it going wrong again has consequences.

Question 2

EMERGENCY SCENARIO — DP2 CONSTRUCTION VESSEL NEAR DRILLING RIG

Vessel: DP2 offshore construction vessel. Location: 120m from a mobile drilling rig, conducting pre-lay survey. Riser and anchor spread deployed from rig. Three gyrocompasses active. Two DGNSS units and one Fanbeam active (Fanbeam tracking reflector on rig). Sea state: 1.5m, wind 18 knots from the north. DPO on watch, approaching end of 10-hour watch. Master in cabin.

--- POINT 1 OF 10 ---

Gyro 2 suddenly reads 201° while Gyros 1 and 3 both read 187°. The DP system shows no alarm — its weighted average heading is 191.7°. The DPO notices the discrepancy on the heading display.

What is the correct immediate action?

Accepted Answer

Manually exclude Gyro 2 from the DP heading input immediately — two gyros agree at 187°, Gyro 2 has clearly jumped. A 4.7° heading error introduced by the weighted average will cause the DP system to apply incorrect thruster forces and may drive the vessel off station toward the rig If the DP system uses weighted averaging rather than true median voting, a 14° gyro jump on one unit produces a meaningful error in the heading output. A 4.7° heading error at 120m from a rig can produce a meaningful sideways force command. More critically, waiting for the DP alarm means accepting the erroneous input for however long the alarm takes to trigger. The DPO has already identified the problem — two gyros agree and one has clearly jumped. The correct action is to manually exclude the outlier immediately, inform the master, and arrange investigation of Gyro 2. The alarm is a safety net, not the trigger for action.

Question 3

Gyro 2 has been excluded. Gyros 1 and 3 are now the only heading inputs. The chief engineer is investigating Gyro 2 and expects a 45-minute assessment. The DP system is now running on two gyros. Position is stable.

With only two gyros now available, what additional operational consideration must the DPO apply?

Accepted Answer

With only two gyros, if Gyros 1 and 3 diverge, there is no way to determine which is correct. The DPO must increase monitoring frequency for heading discrepancy, inform the master of the degraded heading reference status, consider whether the ASOG requires a minimum of three gyros for this operation, and be aware that any future heading divergence between the two remaining gyros will require an immediate decision about whether to continue operations The third gyro is not a luxury — it is the tie-breaker. With three gyros, a divergent reading can be identified and rejected. With two, if they disagree, the DPO has a 50/50 problem with no way to resolve it from the heading data alone. The master must know the heading reference has degraded. The ASOG may specify minimum gyro requirements for different operation types — near a rig with a deployed anchor spread is exactly the type of sensitive operation where three-gyro minimums are commonly set. Running on two gyros 120m from a rig is not automatically acceptable: it requires a formal ASOG status reassessment.