What is defined as parts of the ship that extend beyond the shell and are below the water line?

The term that refers to parts of the ship extending beyond the shell and situated below the waterline is known as appendages. These elements can include various components that contribute to the ship's hydrodynamics and stability, such as rudders, struts, and bilge keels. Understanding appendages is crucial for assessing how they impact the vessel's performance in the water.

While deck fittings refer to items installed on the deck such as hatches, cleats, and winches, and ballast pertains to weight added to a vessel for stability, neither of these options describes parts protruding below the waterline. The keels, on the other hand, serve as a critical structural element running along the bottom of the hull, providing stability and acting as a counterbalance against the forces of wind and waves. However, they are a specific type of appendage rather than a general term for all protruding elements. Therefore, recognizing appendages as the correct term helps in understanding the overall design and functionality of marine vessels.