Ok, we know about sails, masts, rigging, and the basics of those parts. Now let’s put the ship together. The keel is the backbone of the ship. The word "keel" comes from Old English cēol, Old Norse kjóll, ship or keel. Some scholars regard keel as the very first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work De Excidio Britanniae, under the spelling cyulae. This comes from the three ships the Saxons arrived in.

A keel comes in the form of a large strong beam run from the bow of the ship to its stern. In a small wooden ship this was made from a large single tree. In larger wooden ship it was made up of a composite piece of wood from many trees. In today’s steel ship the keel is a large steel beam welded together along the length of the hull. Laying the keel was always an important step in constructing the ship. Since a ship today is built in sections the laying of the keel is considered when the first sheets of steel are cut.

The structural keel provides strength to the ship. It helps to distribute the load the ship is carrying over the entire length of the ship. Because of this fact weapons are made to exploit this design feature. The torpedo of today is designed to explode under a ship thus creating a hole in the water. The ships weight is then focused on the keel where the hole is made. In turn the weight of the ship causes the keel to break. This can lead to the ship physically breaking into two sections.

Another type of keel is the hydrodynamic keel. These are mostly found on sailing vessels. This type of keel is mainly a counter weight for the ship. When the boat rolls in one direction the weight of the keel keeps the boats from turning over. The design if this type of keel varies from vessel to vessel. They are made to be as hydrodynamic as possible to lessen resistance in the water.