A ship's stabilizer generates hydrodynamic or gravitational forces that oppose and neutralize the rolling motion caused by waves and wind. As a wave passes, it creates an unbalanced buoyancy force that induces rolling. A stabilizer counteracts this by applying an equal and opposite torque, utilizing the forward speed of the vessel to create lifting forces or utilizing internal mass to shift the center of gravity. The system continuously detects rolling angles and velocities using sensors or gyroscopes

1. Passive Stabilizers

Passive systems use the natural hydrodynamic flow or movement of a contained mass without requiring external power or complex mechanical control systems

Bilge Keels: Fixed, fin-like projections extending along the lower turn of the ship's hull. When the ship rolls, the water is forced to flow around these keels, creating hydrodynamic drag that dampens the rolling motion.

Passive Anti-Roll Tanks: U-shaped tanks located on opposite sides of the ship partially filled with water. As the ship rolls, the water naturally sloshes from side to side. The tanks are designed with internal restrictions (nozzles/valves) to ensure the water shifts with a phase lag, creating a restoring moment that opposes the wave's rolling action.

2. Active Stabilizers

Active systems utilize dedicated power sources (hydraulics/motors) and automated control mechanisms (gyroscopes) to actively generate corrective forces in real-time.

• Active Fin Stabilizers: Aerofoil-shaped fins protruding from the ship's hull. When a gyro sensor detects a roll, a hydraulic system rapidly pivots the fins to change their angle of attack. The forward motion of the ship passing over the angled fins creates massive lift, forcing one side of the hull up and the other down to counteract the wave.
• Active Anti-Roll Tanks: Similar in structure to passive tanks, but they utilize reversible pumps or blowers to aggressively force the water from one side to the other, creating a faster, more controlled anti-rolling moment independent of the natural roll period.