Question 1

Checking references before re-engaging DP auto, the DPO notices that DGNSS Unit 2 is showing a position 8.5m northeast of Units 1 and 3. It came online after the blackout and its differential correction indicator shows a 40-second-old fix. Unit 1 and Unit 3 are in agreement.

What should the DPO do with DGNSS Unit 2?

Accepted Answer

Exclude Unit 2 from the DP reference inputs until it re-establishes a current differential correction and its position converges with Units 1 and 3. A 40-second-old fix with an 8.5m position offset is not a valid reference in this situation A DGNSS unit with a 40-second-old correction fix showing an 8.5m position offset from two units in agreement is not providing valid position data. Including it as a third reference does not improve accuracy — it introduces an erroneous input that the DP system will partly act upon. Three references where one is wrong is not better than two that agree; the two agreeing references are the reliable inputs. The unit should be excluded and monitored until its fix is current and its position has converged with the other two. This is a direct application of the reference quality management principle: accuracy and confidence, not count, determine reference validity.

Question 2

EMERGENCY SCENARIO — DP2 PLATFORM SUPPLY VESSEL

Vessel: Offshore PSV, DP2 class. Location: 80m from a fixed gas platform, holding position to deliver equipment. DPO on watch. Three DGNSS references active, two gyros operational (Gyro 3 offline for calibration). Sea state: 1.8m, wind 22 knots SW. Thruster configuration: full complement, open bus, consequence analysis test passed 90 minutes ago.

Work through the following 10 decision points in sequence — each builds on the last.

--- POINT 1 OF 10 ---

Without warning, the main generator (G1) trips offline. The DP system sounds an alarm. The bus is still open. The remaining generators (G2, G3) are online and picking up load. Position is currently stable.

What is the DPO's first action?

Accepted Answer

Immediately check the power status panel to confirm which generators are online, verify the bus is still open, and assess whether the remaining power configuration still meets DP2 WCF requirements in the current conditions The DPO's immediate response to any system alarm is active assessment — not passive waiting. Waiting for auto-restart risks losing 30 seconds of situational awareness during which the power situation may worsen. Closing the bus tie immediately is the most dangerous response — it connects both power sections and creates a common cause failure risk. Waiting for the engine room assessment before taking DP action passes decision authority to a team who cannot see the DP system status. The DPO must immediately understand what power is available and whether DP2 capability is maintained with the current thruster configuration and reduced generation.

Question 3

20 seconds after G1 tripped, G2 begins overloading as it attempts to absorb G1's load. G2's frequency is dropping. The power management system (PMS) is attempting to auto-shed non-essential loads. The DPO has confirmed that DP2 WCF may not be maintained if G2 also trips.

What is the DPO's priority action at this point?

Accepted Answer

Inform the master immediately, declare a DP Alert, begin controlled manual thruster reduction on the most loaded thrusters to reduce electrical demand and help stabilise G2, while simultaneously monitoring position At this point the scenario is escalating — the DPO cannot wait for automated systems to resolve it. The master must be informed immediately (this is now a DP Alert situation). Controlled manual reduction of thruster demand on the highest-loaded thrusters removes electrical load while preserving position-keeping capability better than an across-the-board minimum power command (which removes all fine control). Closing the bus in a G2 overload situation is the worst possible action — a fault propagating from G2 would then take out all power simultaneously. The PMS may not shed enough load fast enough; DPO manual intervention is appropriate.