Understanding Dynamic Positioning
 Dynamic positioning (DP) is the technology that enables vessels to maintain position during deepwater operations. Proper maintenance and customization of DP is the key to successful and risk-free operations.
Understanding Specific Classifications
While the advantages of dynamic positioning (DP) operations for deepwater are well-documented and understood, station keeping while under DP is still a complex and evolving science. Understanding the basics of DP, the American Bureau of Shipping (ABS) Classifications for DP and the questions to ask can avoid misunderstandings and potential offshore problems.
Below is a comparison of different ABS Classifications for DP systems (DPS).
| Comparison of Different ABS Classifications For DPS |
| |
| 1. Vessel machinery requirements |
DPS - 0 |
DPS - 1 |
DPS - 2 |
| |
Thrusters/Thruster Prime Movers Rated for Continuous Duty |
Required |
Required |
Required |
| |
Number of Bow Thrusters Needed |
1 |
1 |
2 |
| |
| II. Dynamic Positioning Equipment Requirements |
| |
A. Basic ABS Guidelines |
|
|
|
| |
Central Control Station w/Automatic Heading Control |
Required |
Required |
Required |
| |
Independent Control Station w/Automatic Heading Control |
|
Required |
Required |
| |
Maintain DP Qualified Position with Loss of any Single Point Failure |
|
|
Required |
| |
Transfer of Control |
Not required |
Manually |
Automatically |
| |
| |
B. Environmental Sensors |
|
|
|
| |
Positions referencing Systems Needed |
1 |
2 |
3 |
| |
Wind Sensors |
1 |
2 |
2 |
| |
Gyro Compass |
1 |
2 |
2 |
| |
Vertical Reference Unit |
0 |
1 |
2 |
| |
Signal Processing |
Not required |
Not required |
Required |
| |
| |
C. Miscellaneous Requirements |
|
|
|
| |
Consequence Analysis and DP Alert System |
Not required |
Not required |
Required |
| |
Communications between Bridge and Engine Room Control Station |
1 Means required |
1 Means required |
2 Means
required |
| |
Power Management |
Not required |
Not required |
Required |
| |
Uninterruptible Power Supply |
Not required |
Required |
Required |
| |
Failure Modes and Effects Analysis (FEMA) |
Not required |
Not required |
Required |
Nine Questions to Ask a Vessel Operator About DP
Below are a series of questions to ask a vessel operator to avoid misunderstanding and prevent operation difficulties or misfortune:
- Ask the Operator to provide a short "break down" of the DP configuration for the vessel he proposes.
- Require the Operator to provide DP capability plots for the vessels being proposed. Plot requirements should be standard for the industry. The recommended standard should be as follows. The 1st plot should show 80% thrust, 0-50 knots wind, and 0-2 knots current. The second will show 100% thrust, 0-50 knots wind and 0-2 knots current. Both plots should be at a continuous duty rating. (If an Operator cannot provide these plots, serious consideration should be given as to the Operators' knowledge of his DP equipment and its function aboard his vessel).
- Is the DP system "classed" by a recognized classification society? If so, what is the classification and which society?
- If a DP vessel is "non-classed" ask the Operator if the thrusters are continuous duty rated for the DP plots.
- Does the Operator have a written standard DP operating procedure?
- Does the Operator have a DP performance resume for his fleet?
- Does the Operator have a minimum DP training requirement for his Marine Officers? If so what is that requirement?
- Can he provide résumés or "CVs" for his Marine Officers?
- Are there any cost not carried in the day rate for reference systems or differential signal fees? Contractors of vessels with DP functionality need to ask about hidden costs.
To learn more about DP and the importance of working with industry experts, contact Hornbeck Offshore at (985) 727-2000 or visit www.hornbeckoffshore.com/vessel_osv_dp.html. |
