What is the primary purpose of a bilge keel on a vessel?

The primary purpose of a bilge keel on a vessel is to resist and decrease rolling. Bilge keels are projecting elements found on the hull of some ships, typically running along the length of the vessel near the bottom. Their design helps to increase the vessel's stability by providing a counterforce to the motion of rolling. When the ship begins to tilt or rock side to side, the bilge keels generate hydrodynamic resistance in the water, which slows down this movement. This is particularly important for maintaining comfort and safety on board, especially in rough seas, as excessive rolling can lead to hazardous situations for both the vessel and its occupants.

While bilge keels can have secondary effects that may influence fuel efficiency positively by allowing smoother travel through the water, their main function is specifically tied to roll reduction. Enhancements to underwater visibility and additional storage are not functions typically associated with bilge keels.