What does 'freeboard' refer to in a vessel?

Freeboard refers to the vertical distance measured from the waterline to the upper edge of the hull, specifically the gunwale, which is the upper edge of the side of the boat. This measurement is crucial as it indicates how high a boat sits above the water and provides insight into its stability and safety.

A higher freeboard generally means that the vessel is less likely to take on water, thus enhancing its seaworthiness, especially in rough conditions. It can also affect how easily the vessel can be boarded or exited. Understanding freeboard is important for operators and owners, as it can influence decisions regarding loading, balance, and overall vessel performance.

The other options describe different aspects of a vessel's design or characteristics but do not provide the correct definition of freeboard. For example, the distance from the bow to the stern relates to the overall length of the boat, while the thickness of the hull pertains to the structural elements of the vessel, and structural integrity concerns the strength and durability of the boat itself.