Fin stabilizers

Fin stabilizers, sometimes called fin drives, are passive roll stabilizers. They are located below the waterline at the bottom of the ship's hull and provide additional stability by preventing the ship from rolling. They are often installed on passenger ships to increase passenger comfort.

Fin stabilizer device

Two fin stabilizers are installed on ships and vessels, one on the starboard side and one on the port side. Each device is housed in a waterproof box. The fin blade is attached to a support connected to a rotary mechanism. There is a movable part (flap) at the edge of the fin rudder that controls the water flow. The stabilization system is controlled from the control panel on the navigation bridge, where local indication and control are also provided.

Fin rudder with movable part (flap)

How a fin stabilizer works during rolling motion

When the sea is rough, stabilizers extend from technological pockets located on both sides of the hull. The fins are adjusted depending on sea conditions, changing the angle of inclination within 25 degrees, using a computer-controlled gyroscope. An electric motor controls two piston pumps located on different sides, which alternately pump pressure, supplying hydraulic fluid from side to side. The hydraulic power unit rotates a rotary mechanism that controls the movements of the supports to which the fin rudders are welded. The fin rudder rotates on its axis, and together with the up-down movement of the flaps, a hydrodynamic effect is created that reduces the ship's roll by almost 90 percent.

Diagram of the fin stabilizer device

When operating stabilizers, many variables must be taken into account: wind, waves, ship movement, and draft. Fin stabilizers are much more effective at higher speeds and lose effectiveness when the ship is traveling at minimum speed.