Aux 2 Unit 3 Q4

Hydraulic actuators are often preferred for vessel stabilizers over electrical actuators due to several key advantages that make them well-suited for this demanding application:

1. High Power Density: Hydraulic systems can generate and transmit high forces and torques in a relatively compact and lightweight package. This is crucial for stabilizers, which need to counteract significant rolling forces generated by waves. Electric actuators, especially at comparable power levels, can be bulkier and heavier.  
2. Smooth and Precise Control: Hydraulic systems offer smooth and precise control of actuator movement, essential for fine-tuning the stabilizer fins’ position to counteract the vessel’s roll motion effectively. Electric actuators, while also capable of precise control, may exhibit some jerkiness or lag, particularly at low speeds or during frequent direction changes.  
3. Robustness and Durability: Hydraulic actuators are inherently robust and can withstand harsh marine environments, including exposure to saltwater, humidity, and vibrations. Their sealed construction protects internal components from the elements, ensuring reliable operation even in challenging conditions. Electric actuators, with their exposed electrical components, might be more susceptible to corrosion and damage in a marine environment.  
4. Overload Protection: Hydraulic systems incorporate pressure relief valves that act as safety mechanisms, preventing damage to the system and the stabilizer fins in case of excessive loads or sudden impacts. Electric actuators may require additional protective measures to prevent damage from overload conditions.
5. Self-Lubrication: Hydraulic fluid acts as a lubricant for the system’s internal components, reducing friction and wear. This contributes to the longevity and reliability of the hydraulic actuator, requiring less frequent maintenance compared to electric actuators, which may need periodic lubrication of bearings and gears.  
6. Fail-Safe Operation: Hydraulic systems can be designed with fail-safe features, such as counterbalance valves or accumulators, that can hold the stabilizer fins in a safe position in case of power loss or hydraulic system failure. This prevents uncontrolled movement and enhances safety in critical situations.
7. Established Technology and Expertise: Hydraulic systems have a long history of use in marine applications, and there’s a vast pool of experienced engineers and technicians familiar with their installation, operation, and maintenance.

While electric actuators have their advantages, such as potential energy efficiency and cleaner operation, the specific demands of vessel stabilization often favor the use of hydraulic actuators due to their superior power density, robustness, and control capabilities in the harsh marine environment.

Let’s outline a hydraulic circuit suitable for controlling a single stabilizer fin within a constant pressure hydraulic system commonly found on vessels.

Core Principle:

• A constant pressure hydraulic system maintains a consistent pressure within the fluid lines, even when the stabilizer isn’t actively moving.
• This allows for quick response when adjustments are needed to counteract the vessel’s roll.

Key Components and Functions:

1. Hydraulic Pump:
   • Supplies pressurized fluid to the system.
   • Typically a fixed-displacement type (e.g., gear pump) to ensure constant flow and pressure.
2. Hydraulic Reservoir (Tank):
   • Stores the hydraulic fluid.
   • Allows for heat dissipation and air separation.
3. Stabilizer Actuator (Cylinder):
   • Double-acting cylinder that directly controls the fin’s movement (up or down).
4. Directional Control Valve:
   • A 4/3-way valve (4 ports, 3 positions) that directs fluid flow to either side of the actuator, controlling its extension or retraction.
   • Center position is typically “closed” to hold the fin in place.
5. Relief Valve:
   • Safety valve that opens if pressure exceeds a safe limit, protecting the system from damage.
   • Maintains constant pressure when the system is idle.
6. Flow Control Valve:
   • Optional, but often included to regulate the speed of fin movement.
   • Restricts fluid flow, allowing for smoother and more controlled adjustments.
7. Check Valves:
   • Prevent backflow of fluid, ensuring the fin stays in position when the directional valve is neutral.
8. Filters:
   • Protect the pump and other components by removing contaminants from the fluid.
9. Piping and Hoses:
   • Connect the various components.
   • Must be rated for the system’s operating pressure.

Circuit Operation:

1. Idle/Neutral:
   • Pump runs continuously, maintaining pressure.
   • Directional valve in center (closed) position, holding the fin in its current position.
   • Excess pump flow goes over the relief valve back to the tank.
2. Fin Adjustment (e.g., Upward):
   • Control system (likely electronic, based on motion sensors) signals the directional valve.
   • Valve shifts, sending pressurized fluid to the bottom side of the actuator cylinder.
   • Piston extends, pushing the fin upwards.
   • Fluid from the top side of the cylinder returns to the tank, possibly through the flow control valve to regulate speed.
3. Holding Position:
   • Once the desired fin angle is reached, the control system returns the directional valve to neutral.
   • Check valves trap the fluid, holding the fin in place.
   • System returns to idle state.
4. Reverse Movement (Downward):
   • Similar to upward movement, but the directional valve directs fluid to the opposite side of the actuator.

Safety Considerations:

• Overload Protection: System should have safeguards to prevent excessive loads on the actuator and fin.
• Emergency Stop: Provision to quickly stop fin movement in critical situations.
• Regular Maintenance: Essential for ensuring reliability and preventing leaks.

Remember, this is a simplified description. Actual systems may include more components for advanced control and integration with other ship systems.