Keel
The Keel is the principal structural member running along the very bottom of a ship's hull, from bow to stern — effectively the vessel's backbone, to which the frames and the rest of the hull structure are attached. Laying the keel traditionally marks the start of a ship's construction (the “keel-laying”), and it is the reference from which a ship's draft is measured (waterline to the bottom of the keel).
On sailing yachts the keel also refers to a weighted fin projecting below the hull that provides stability (resisting heeling) and lateral resistance (stopping sideways drift, or leeway). On ships, structural variants include the flat plate keel, bar keel and duct keel, and a bilge keel is an external fin that reduces rolling. The keel is a foundational structural and design element of any vessel — the spine on which the hull is built. It is fundamental to a ship's strength and, on sailing craft, its stability.
The keel is the ship's backbone — the structural spine the whole hull is built on, the mark of a ship's birth (keel-laying), and the datum for measuring draft. On sailing craft it also provides the stability and grip that let a boat sail upwind. It is as fundamental to a vessel as a spine is to a body.
What does the keel do?
It is the structural backbone along the bottom of the hull; on sailing yachts a weighted keel also gives stability and resists sideways drift.
What is keel-laying?
The traditional start of a ship's construction, when the keel is laid down as the foundation of the hull.