Question 1

CONTINUING: Vessel has drifted to 280m south of platform and is decelerating. Speed is now 0.3kt southward. The drift will stop naturally in approximately 2 minutes. How should the DPO manage the final arrest of drift?

Accepted Answer

Apply gentle, graduated northward joystick input (not maximum thrust) to assist the deceleration and bring the vessel to a stop at the current position — do not attempt to drive back toward the original setpoint yet; the priority is controlled stop, not position recovery Controlled stop first, position recovery second — this is the correct post-drive-off priority sequencing. Driving immediately back to 60m from the platform with AZ1 isolated and the fault not yet understood would be moving toward the platform with degraded capability. A stable stop at a safe distance is the correct holding position while the consequence analysis is done.

Question 2

SCENE: DP2 PSV holding 60m south of a fixed gas platform, Hs 1.8m from north, wind 18kt NNW. All thrusters online. DP auto, ASOG green. 0347: Without warning, the vessel begins accelerating slowly south. DP position readout shows growing offset. AZ1 shows 98% demand to the south — the same direction the vessel is moving. Environmental forces are from the north. What does this pattern indicate and what is the DPO's immediate conclusion?

Accepted Answer

This is a probable drive-off: AZ1 is producing maximum thrust away from the setpoint, opposite to the environmental force direction — instead of fighting the northerly forces, AZ1 is amplifying the southward movement. The DP system should be demanding northward thrust from AZ1; the 98% south demand confirms a runaway thruster, not a DP system corrective response The drive-off signature is: maximum thruster demand in the direction of movement, opposite to environmental force. With a 18kt NNW wind and 1.8m northerly swell, AZ1 should be demanding northward thrust to hold position — 98% southward demand is the textbook thruster runaway pattern. Every second spent waiting while AZ1 is at full runaway thrust is another metre toward open water south, away from the platform. The DPO must recognise this in the first 15 seconds.

Question 3

CONTINUING: Vessel is accelerating south with AZ1 at 98% south demand. The DPO has 20–25 seconds before the vessel's southward momentum becomes difficult to arrest without risking overshooting toward open water. What is the correct first physical action?

Accepted Answer

Manually stop AZ1 at the thruster control panel to remove the erroneous drive force, then assess remaining thruster status — only after AZ1 is stopped should joystick or manual mode be considered; switching to joystick with AZ1 still running south just adds counter-thrust to a fight you may not win fast enough Stopping the runaway thruster removes the erroneous force. Switching to joystick before stopping AZ1 means the DPO is now trying to overcome AZ1's full southward thrust with the remaining thrusters, potentially in a losing fight against the momentum already built. Motor protection on emergency stop is handled by the thruster controller — a manual stop is not a free-spin stop and will not mechanically damage the thruster in normal circumstances.