The backbone of the ship runs along the bottom. The keel is the central structural member extending longitudinally along the baseline of the hull, from which the frames and plating rise.

In traditional construction the keel was a heavy timber or steel bar; in modern ships it may be a plate keel or a more complex structure integrated with the double bottom. The keel contributes to longitudinal strength and to directional stability. Bilge keels, fitted along the turn of the bilge, reduce rolling but are separate from the main keel.

Grounding damage often concentrates on the keel and the bottom structure around it. Drydock inspections pay close attention to keel blocks and the condition of the keel plate. The keel’s alignment is fundamental to the fair form of the entire hull.

• Central longitudinal structural member at the bottom of the hull
• Foundation for frames and plating
• Contributes to strength and directional stability
• Vulnerable in groundings and closely inspected in drydock