Dynamic Positioning (DP) systems are central to modern vessel operations, allowing for precise control over a vessel's position and heading. These systems utilize various Operational Modes to handle different tasks and operational conditions, ensuring the vessel remains in the right position and heading at all times. However, it's important to note that while a vessel may have multiple modes available, it can only be under the control of one mode at a time.
In this blog, we will break down the different operational modes available in a typical DP system and explore their unique functionalities and applications.
DP (Dynamic Positioning)
In DP mode, the vessel’s heading and position are both automatically controlled and maintained. This mode is typically used when the vessel needs to stay fixed in relation to a stationary target with a set heading, such as when performing offshore tasks like drilling or pipe laying.
Joystick Manual Heading (JSMH)
In this mode, the vessel is manually controlled using the joystick. The operator controls forward/aft and port/starboard movements, while a turning knob adjusts the vessel's heading around its center. This mode is ideal for situations where full manual control is necessary.
Joystick Auto Heading (JSAH)
This mode still allows manual control of fore/aft and port/starboard movement, but the vessel's heading is automatically maintained. It’s often used for close maneuvering when precise control over position is necessary but without manual heading adjustments.
Min Power/Weathervaning
This mode is designed to minimize power consumption by maintaining the vessel's heading into the prevailing weather. While DP control is still active, it allows for efficient use of power, which is particularly beneficial in rough weather conditions.
ROV Follow
The vessel's position is automatically controlled to track a moving target, such as a Remotely Operated Vehicle (ROV). The system ensures the vessel stays within a defined area relative to the ROV, maintaining a stable position as the ROV moves.
Auto Pilot
This mode uses the vessel’s main propulsion and rudder to move along a fixed course. Typically used during transit, it allows the vessel to follow a set course with automatic heading control.
Auto Sail
Similar to Auto Pilot, this mode uses the main propulsion and rudder to maintain a set track with heading control. Azimuth thrusters can be substituted for the main propeller and rudder, providing greater flexibility in certain situations.
Auto Speed
In Auto Speed mode, the vessel’s forward and lateral speeds are controlled automatically, maintaining a constant low speed with the help of Doppler log signals and automatic heading control.
Auto Track
In Auto Track mode, the vessel moves automatically along a pre-determined path or track, between two or more waypoints. The heading is automatically controlled to ensure the vessel stays on course, making it ideal for transit operations.
DP systems offer other specialized modes to cater to specific vessel roles and operational needs:
Model Control
In this mode, the DP system continues operating even in the case of a failure in position or heading sensors, ensuring that the vessel remains in its current operational mode despite any technical issues.
Simulation
This offline mode is used for training and testing purposes. It simulates input/output data across all modes to help operators familiarize themselves with the system without affecting actual operations.
Pick-up/Fixed Loading
This mode is typically used by shuttle tankers, where the vessel’s heading and position are controlled based on prevailing weather, allowing it to stay in place for loading operations.
Approach/Loading
Similar to Pick-up/Fixed Loading, this mode maintains the vessel’s position at a fixed radius from a reference point, ensuring it stays in place during loading or unloading tasks.
Riser Follow
This mode is often used in drilling vessels, where the vessel's position is controlled to maintain a consistent riser angle, ensuring safety during drilling operations.
Before switching into any DP mode, the system checks that the necessary equipment is available and properly selected. For instance, to engage DP mode, the system will confirm that the correct thrusters, gyrocompass, and position measurement equipment (PME) are all ready for use. This ensures smooth operation and minimizes the risk of equipment failure.
Operational modes in Dynamic Positioning (DP) systems are designed to provide the right level of control for various vessel roles and tasks. From full manual control to automated track-following, each mode serves a unique purpose, allowing vessels to maintain position, heading, and speed with remarkable precision. Understanding these modes is crucial for optimizing vessel operations in the offshore industry, improving safety, and ensuring that tasks are completed efficiently and accurately.
