A keel is a structural element on the bottom of a boat that runs from bow to stern. It serves several purposes, including providing sideways resistance to counter the force of the wind, preventing the boat from being blown sideways, and keeping the vessel upright. The keel can be made of various materials, including timber, metal, fiberglass, and aluminum. There are different types of keels, including:
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Flat plate keel: This is the most common type of keel, found in the majority of ocean-going ships and other vessels.
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Full keel/ballast keel: This is a vertical downward extension of the boats hull, narrowly V-shaped, and usually ballasted or weighted for stability and lateral resistance.
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Fin keel: This is a high-performance, low-drag appendage that is usually cast in lead and bolted to the flattish bottom of the hull. It is intended to steady the boat and make it handy to steer.
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Bilge keel: This is one of a pair of short keels fitted to the bilge of a boat, usually to reduce rolling.
In sailboats, keels serve two purposes: minimizing the lateral motion of the vessel under sail (leeway) and counteracting the lateral force of the wind on the sail(s) that causes rolling to the side (heeling) .
