No, dynamic positioning (DP) systems typically do not directly measure the sea current. While these sophisticated systems are designed to maintain a vessel's position and heading automatically, they primarily focus on directly measuring and compensating for certain key external forces.
A Dynamic Positioning (DP) system is a computer-controlled system that automatically maintains a vessel's position and heading by using its own propellers and thrusters. This system processes data from various sensors to counteract environmental forces that could cause the vessel to drift.
How DP Systems Handle External Forces
Modern DP control systems are designed to manage several external forces that impact a vessel's stability and position. However, not all forces are directly measured by the system itself.
- Directly Measured Forces: Most modern DP control systems primarily focus on directly measuring and compensating for wind forces acting on the vessel. This is typically achieved using anemometers that provide real-time wind speed and direction data, allowing the system to immediately adjust thrust to counteract wind-induced drift.
- Forces Not Directly Measured by the DP System: Forces such as water current, wave slap, and forces from coupled bodies (e.g., a connected riser or another vessel) are generally not directly measured by the DP control system. Instead, the DP system infers the cumulative effect of these unmeasured forces by continuously monitoring the vessel's position and heading relative to a setpoint.
This means that while the DP system effectively compensates for the impact of sea currents and waves on the vessel's position, it does so by observing the resulting deviation from the desired location rather than by directly sensing the current's speed and direction with a dedicated sensor.
Components and Compensation Mechanism
DP systems rely on a network of sensors and a powerful control computer to achieve precise positioning. Here's a breakdown of how they operate:
| Force Type | Measurement Method | Compensation Method |
|---|---|---|
| Wind | Direct measurement via anemometers | Immediate feed-forward adjustment of thruster forces |
| Water Current | Not directly measured by the DP control system | Inferred from vessel's position deviation; feedback control |
| Wave Slap | Not directly measured by the DP control system | Inferred from vessel's position deviation; feedback control |
| Coupled Body Forces | Not directly measured by the DP control system | Inferred from vessel's position deviation; feedback control |
Practical Insight: The DP system's ability to maintain position despite unmeasured forces is due to its sophisticated feedback loop. It constantly receives position data from global navigation satellite systems (GNSS) like GPS or DGPS, alongside other position reference systems (e.g., hydroacoustic positioning, taut wire). If the vessel starts to drift due to current or waves, the system detects this position error and calculates the necessary thruster adjustments to bring it back to the target location. This continuous adjustment process effectively counteracts all environmental forces, regardless of whether they are directly measured.
For more comprehensive information on dynamic positioning systems, you can refer to reputable sources such as DNV or Marine Insight.
