What is the primary function of bilge keels?

Bilge keels are specialized stabilizing structures mounted on the sides of a vessel below the waterline. Their primary function is to reduce the rolling motion of the vessel, particularly when it's in rough seas or adverse weather conditions. By extending outward from the hull, bilge keels create additional hydrodynamic resistance which helps dampen the lateral motion of the ship as it encounters waves, ultimately enhancing the overall stability and comfort for those onboard.

While some options may align with the overall functionality of a vessel, they do not pertain specifically to the purpose of bilge keels. For example, enhancing speed during navigation is typically achieved through streamlined hull designs and propeller efficiency rather than through stability features like bilge keels. Improving cargo space is more related to the design and layout of the ship's interior rather than to any external features like bilge keels. Lastly, assistance in docking maneuvers often involves rudders, propellers, and thrusters, and is not a function served by bilge keels which are more focused on stability at sea rather than maneuverability in a docking scenario.