The false keel was a timber, forming part of the hull of a wooden sailing ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

. Typically 6 inches thick for a 74-gun ship in the 19th century, the false keel was constructed in several pieces, which were scarphed together, and attached to the underside of the keel

Keel

In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

by iron staples. The false keel was intended to protect the main keel from damage, and also protect the heads of the bolts holding the main keel together. The false keel could easily be replaced when it became damaged.