Stabilizer Systems | Electropneumatic S.A.

Stabilizer Systems

A ship’s movements at sea encompass six degrees of freedom: Roll, Heave, Pitch, Yaw, Sway and Surge.

Among these movements, rolling stands out as a significant challenge that can be effectively managed through various techniques like installing bilge keels, anti-rolling tanks or stabilizers. Stabilizing systems are strategically integrated into ships to mitigate rolling motions by applying forces in opposing directions.

Two primary types of stabilizing systems are employed on ships:

  1. Fin Stabilizers:These systems use fins to counteract rolling motions, ensuring a more stable and comfortable sailing experience.
  2. Tank Stabilizing System:This setup employs specially designed tanks filled with water to create a balancing effect, thereby reducing the ship’s rolling motion.

By implementing these stabilizing techniques, ships can navigate challenging waters with increased stability and passenger comfort, ensuring safer and smoother journeys.

Fin Stabilizers: How They Work

The fins’ stabilizing force is generated by their movement through the water, creating both drag force and lift due to the flow of water above and below the hydrofoil shape.

  • Zero Angle of Attack:When the ship maintains no rolling movement, the fins stay at a 0° angle, offering no lift or push force, as depicted in the figure above.
  • Negative & Positive Angle of Attack: As the ship begins rolling (detected by sensors), if the ship rolls to the port side, the port fin tilts upwards (Negative Angle of Attack), experiencing Negative lift or a push from the bottom. Simultaneously, the starboard fin tilts downwards (Positive Angle of Attack), resulting in a pull towards the starboard side. The combined forces counteract external forces attempting to tilt the ship, stabilizing its motion.
  • Fin Movement Control: For efficient stability, automatic control of fin movement is critical in ship stabilizing systems. Basic systems use small gyroscopes, generating forces proportional to ship roll velocity. These forces are amplified hydraulically to adjust the fin angle. More sophisticated systems employ vertical and velocity gyroscopes, controlling the fin angle based on roll angle, velocity, and acceleration. Compensated control systems stabilize the ship around its mean roll point, reducing power demand for propulsion and stabilization.
Thicker Lines = Hydraulic Lines, Thinner Lines = Electrical Lines, SCP = SOLAS Control panel, BCP = Bridge Control Panel, L = Ship’s Log, RIP = Remote Indicator Panel, SA = Ship’s Automation, LUB = Lube Oil Tank, CCU = Central Control Unit, RSU = Roll sensor Unit, LCU = Local Control unit, HPU = Hydraulic Power Unit, FU = Fin Unit.

RSU – Roll Sensor Unit (Compensated control system)

These units enable roll reduction of over 90%, typically reducing 30° out-to-out rolls to less than 3°. However, the stabilizing power varies with the square of the ship’s speed. Fins are least effective at low or zero speeds, acting similarly to additional bilge keels.

Implementing these advanced stabilizing techniques enhances a ship’s stability, making voyages safer and more comfortable, particularly in challenging sea conditions.