A structural keel is a beam around which the hull of a ship is built. The keel runs in the middle of the ship, from the bow (FRONT) to the stern (REAR), and serves as a basic foundation or spine of the structure, providing the major source of structural strength of the hull.
The keel is generally the first part of a ship's hull to be constructed. The picture illustrates a sail boat keel. This type of keel will give more stability in the water which, is also refers to the vessels drought, or also called draft.
Modern ships are now largely built in a series of pre-fabricated, complete hull sections rather than being built around a single keel.
If a ship suffers severe structural stress that usually would happen during a ship wreck when running aground, it is possible for the keel to break or be strained to the extent that it loses structural integrity. In this case the ship is commonly said to have broken its back. This type of damage / failure means that the entire structure of the ship and its machinery has been compromised and repairing such damage would require generally require re-building the ship from the ground up. A ship that has broken its back is almost certainly is usually found
not salvageable and subsequently written off by its insurers.