The keel is the main longitudinal structural member running along the centerline of a ship’s bottom, from bow to stern. It’s the structural backbone from which the rest of the hull framework is built.
Structural Role
The keel provides the primary longitudinal strength along the ship’s bottom centerline, resisting the bending stresses (hogging and sagging) that a ship experiences moving through waves. It also provides a strong central reference line for attaching frames, floors, and bottom plating during construction.
Types of Keel
- Flat plate keel — the standard on most modern merchant ships; a flat steel plate forming the lowest part of the hull, integrated with the bottom shell plating
- Bar keel — a solid bar-shaped keel, more traditional, still used on some smaller vessels
- Duct keel — a keel structure with an internal void space used to route pipework, common on larger vessels
”Laying the Keel”
In traditional shipbuilding, “laying the keel” marked the official start of a ship’s construction and was historically used as the vessel’s official build date. In modern block-construction methods, this milestone is less structurally central than it once was, but the term remains in industry use.
Exam Relevance
Keel types and their role in overall hull strength are part of ship construction and naval architecture topics covered in deck and engineering officer competency exams.