While the advantages of 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 ABS Classifications for DP and the questions
to ask can avoid misunderstandings and potential offshore
problems.
| COMPARISON
OF DIFFERENT ABS CLASSIFICATIONS FOR DPS |
Click
here to download this chart is a pdf format. |
|
| 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 |
| |
Uninterruptible Power
Supply |
Not required |
Required |
Required |
| |
|
TYPICAL
DYNAMIC POSITIONING SYSTEM - CLASS 0
Click
here to download schematic in a pdf format
TYPICAL DYNAMIC POSITIONING SYSTEM - CLASS 1
Click
here to download schematic in a pdf format
TYPICAL DYNAMIC POSITIONING SYSTEM - CLASS 2
Click
here to download schematic in a pdf format
Illustrations reproduced
courtesy of Nautronix, Ltd.
NINE
QUESTIONS TO ASK A VESSEL OPERATOR ABOUT DP
- 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
resumé 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.
