DPO Operation & Vessel Maneuvering 3 — Questions and Answers
Question 1: A DP operator is planning an operation near an FPSO. Which environmental factor requires the most careful assessment regarding vessel interaction?
- Atmospheric pressure changes
- The FPSO's own wave and current shadow effects (Correct answer)
- Air temperature effects on thruster efficiency
- Seabed reflectance affecting DGPS signals
Correct answer: The FPSO's own wave and current shadow effects
Large floating structures like FPSOs create current and wave shadow zones that significantly alter the environmental forces experienced by the DP vessel operating nearby.
Question 2: During a DP operation the watchkeeper observes high 'model error' values in the DP controller display. This MOST likely indicates:
- The DP model correctly predicts vessel behavior
- Unmodeled external forces or incorrect environmental inputs are affecting the vessel (Correct answer)
- The thruster system is operating above its rated capacity
- A loss of acoustic position reference signal
Correct answer: Unmodeled external forces or incorrect environmental inputs are affecting the vessel
High model error indicates the DP controller's mathematical model is not matching actual vessel behavior, typically due to unmodeled forces or inaccurate environmental inputs.
Question 3: What is the correct procedure when a DP vessel experiences a blackout during a critical subsea operation?
- Immediately anchor the vessel to prevent drift
- Follow the Emergency Shutdown procedure and notify the installation (Correct answer)
- Switch all thrusters to manual control and maintain position
- Continue operations using only battery backup systems
Correct answer: Follow the Emergency Shutdown procedure and notify the installation
A blackout during critical DP operations requires immediate execution of the Emergency Shutdown procedure and notification to the installation due to risk of loss of position.
Question 4: The term 'footprint' in DP operations refers to:
- The area of seabed disturbed by the vessel's anchors
- The boundary of acceptable vessel excursion around the target position (Correct answer)
- The physical size of the vessel's hull at the waterline
- The coverage area of the vessel's DGPS antenna array
Correct answer: The boundary of acceptable vessel excursion around the target position
Footprint defines the maximum allowable deviation from the target position in any direction, beyond which the operation must be suspended.
Question 5: When operating a DP vessel in shallow water, the operator should anticipate that thruster efficiency will:
- Increase due to reduced water resistance above the thrusters
- Decrease due to interaction between thruster wash and the seabed (Correct answer)
- Remain unchanged as long as thruster RPM is constant
- Increase because the current speed is lower near the seabed
Correct answer: Decrease due to interaction between thruster wash and the seabed
In shallow water, thruster wash reflects off the seabed and recirculates back into the thruster intake, reducing effective thrust output significantly.
Question 6: A DP operator must document an 'activity-specific operating guideline' (ASOG) before each operation. Its primary purpose is to:
- Record fuel consumption targets for the operation
- Define operational and technical limitations and the criteria for suspension (Correct answer)
- Specify the watch schedule for the DP operators
- Document the vessel's position reference system calibration data
Correct answer: Define operational and technical limitations and the criteria for suspension
The ASOG defines the technical and operational criteria under which the operation may proceed, be downgraded, or must be suspended, ensuring a pre-agreed response to changing conditions.
Question 7: When using a Fanbeam laser position reference system, the operator should be aware that its accuracy degrades when:
- The vessel is stationary for extended periods
- Atmospheric haze, rain, or smoke obscures the line of sight to the prism (Correct answer)
- The vessel's heading changes by more than 10 degrees
- The water depth exceeds 200 meters
Correct answer: Atmospheric haze, rain, or smoke obscures the line of sight to the prism
Fanbeam is an optical system and its signal is attenuated or lost when visibility is reduced by atmospheric conditions such as rain, fog, or smoke.
DPO Operation & Vessel Maneuvering 3
A DP operator is planning an operation near an FPSO.
Which environmental factor requires the most careful assessment regarding vessel interaction?