directional instability

Directional instability in nautical science refers to a ship's tendency to deviate from a set course, which can increase even without external forces. While a directionally unstable ship is easier to maneuver, a stable ship requires less effort to maintain its course. A compromise between these extremes is generally preferred in ship design.1

A ship's underwater profile can offer a general indication of its directional stability; if the hull's area is concentrated towards the stern, it's likely to be more stable. However, stability or instability doesn't eliminate the need for steering devices. The most common is a rudder, typically located at the stern, which generates lift when turned to alter the ship's direction. For enhanced maneuverability, especially at low speeds, ships may be equipped with bow thrusters, which are propellers in transverse tunnels near the bow that can push the bow sideways without causing forward motion.1