Question 1

The chief engineer reports that Gyro 3's fault is now identified: a power supply card has failed. On investigation, he also discovers that Gyros 2 and 3 share the same UPS unit — the UPS itself is now showing a charging fault. Gyro 1 is on a separate UPS.

What does the common UPS for Gyros 2 and 3 represent, and what must the chief engineer check immediately?

Accepted Answer

Gyros 2 and 3 sharing a UPS is a common cause failure path — a single UPS fault can simultaneously take out both units. The chief engineer must immediately verify that the UPS charging fault has not degraded the UPS capacity such that Gyro 1's UPS is also at risk, and the FMEA must be reviewed to determine whether this shared UPS arrangement was an identified or unidentified CCF A shared UPS for two of three gyrocompasses is a common cause failure path that removes the voting benefit of having three gyros. If the UPS fails, both Gyros 2 and 3 fail simultaneously — leaving only Gyro 1 as the sole heading reference with no comparison possible. This is exactly the CCF concept that IMCA M103 FMEA guidance addresses. The discovery of this shared UPS during an active incident suggests this was either an unidentified CCF or a known CCF that was accepted without adequate mitigation. The chief engineer must assess whether the degraded UPS creates an immediate risk to Gyro 2 and 3 (already failed) or to Gyro 1's UPS as well.

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.