What shape does the keel commonly take on a vessel?

The keel of a vessel commonly takes on a flat shape, particularly in many types of boats and modern vessels. This design allows for improved stability and effective tracking through the water. A flat keel provides a larger surface area beneath the waterline, which helps prevent excessive rolling and contributes to the overall balance of the vessel while it is underway.

Additionally, a flat keel is essential for sailboats as it aids in maintaining the boat's direction when sailing upwind by reducing sideways drift. The flat shape is also easier to construct, which can be advantageous in terms of manufacturing.

While other shapes like cylindrical, curved, or pointed do exist in various boat designs, these are less common for keels meant to provide stability and direct movement in the water. For instance, a pointed keel might be found in some racing or specialized craft designed for speed, but it does not serve the dual purpose of stability and directional control as effectively as a flat keel.